---
title: "Signatures — React"
description: "Sign documents with a drawn, typed or uploaded signature and a key you control, check the signatures a document has, and warn before an edit breaks one."
framework: "React"
source: "https://www.embedpdf.com/docs/headless/react/forms/signatures"
---

# Signatures

A digital signature has two parts: the **mark**, what people see in the signature field, such as a
drawn signature; and the **key**, which seals the document so any later change shows. The signature
plugin signs with both, checks the signatures a document already has, and warns before an edit would
break one.

Register `signaturePlugin()` next to `formPlugin()` and `stampPlugin()`, with the key to sign with:

**`basic.tsx`**

```tsx
import { useEffect, useRef, useState } from 'react';
import { Viewer, DocumentGate, usePageList } from '@embedpdf/react/runtime';
import type { OpenInput } from '@embedpdf/react/runtime';
import { Stage, stagePlugin, useStage } from '@embedpdf/react/stage';
import { RenderLayer, renderPlugin } from '@embedpdf/react/render';
import { interactionPlugin } from '@embedpdf/react/interaction';
import { FormLayer, formPlugin, useForm, useFormState } from '@embedpdf/react/form';
import { stampPlugin, useStamp, useStampAssetPreviewUrl } from '@embedpdf/react/stamp';
import {
  createTestSigner,
  signaturePlugin,
  useSignature,
  useSignatureState,
  useSignerRows,
} from '@embedpdf/react/signature';
import { localEngine } from '@embedpdf/engine';

import './basic.css';

const engine = localEngine();
const assetEngine = engine; // a person's marks are stamps, kept as PDFs; they open here too
// A throwaway key for the demo. Bring your own with `webCryptoSigner`, a
// service with `remoteSigner`, or a person's own with `personalSigner`.
const signer = createTestSigner({ commonName: 'Ada Lovelace' });
const plugins = [
  stagePlugin(),
  renderPlugin(),
  interactionPlugin(),
  formPlugin(),
  stampPlugin({ assetEngine }),
  signaturePlugin({
    key: () => signer,
    // Trust the demo key itself, so its signatures check out as 'valid'.
    trust: { anchors: async () => [(await signer).certificate] },
  }),
];

const ebook = async (): Promise<OpenInput> => {
  const response = await fetch('https://snippet.embedpdf.com/ebook.pdf');
  return { kind: 'bytes', id: 'ebook', bytes: new Uint8Array(await response.arrayBuffer()) };
};

/**
 * The ebook has no signature field, and the browser holds no signatures yet:
 * add a field to the last page, and one person with a typed signature.
 */
function useSetUp() {
  const form = useForm();
  const stamp = useStamp();
  const stage = useStage();
  const status = useFormState((state) => state.status);
  const page = usePageList().at(-1)?.ref;
  const done = useRef(false);

  useEffect(() => {
    if (status !== 'ready' || !page || done.current) return;
    done.current = true;
    void (async () => {
      await form.create({
        family: 'signature',
        name: 'approval',
        widgets: [{ page, rect: { x: 72, y: 560, width: 220, height: 64 }, color: '#94a3b8' }],
      });
      stage.goToPage(page);
      const { library } = await stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
      await stamp.createAsset({
        libraryId: library.id,
        name: 'signature',
        label: 'Signature',
        mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
      });
    })();
  }, [form, stamp, stage, status, page]);
}

function MarkButton({ assetId, label, onPick }: { assetId: string; label: string; onPick: () => void }) {
  const url = useStampAssetPreviewUrl(assetId);
  return (
    <button type="button" className="button" title={label} onClick={onPick}>
      {url ? <img src={url} alt={label} className="preview" /> : label}
    </button>
  );
}

function SignBar() {
  useSetUp();
  const signature = useSignature();
  const [person] = useSignerRows();
  const { signatures, target, busy } = useSignatureState();
  const field = useFormState((state) => state.fields.find((candidate) => candidate.family === 'signature'));
  const [error, setError] = useState<string | null>(null);
  const signed = signatures[0];

  // The target is the field someone clicked; without one, the form's signature field.
  const sign = (assetId: string) => {
    const destination = target ?? field?.ref;
    if (!destination) return;
    setError(null);
    signature
      .placeMark({ assetId }, { field: destination })
      .catch((reason: Error) => setError(reason.message));
  };

  let status = 'Click the field, or pick the signature';
  if (!person || !field) status = 'Getting ready…';
  else if (error) status = error;
  else if (busy) status = 'Signing…';
  else if (signed) status = `Signed by ${signed.signer.name}: ${signed.verdict?.summary ?? 'checking…'}`;
  else if (target) status = 'Now pick the signature';

  return (
    <div className="toolbar">
      {person?.signatures.map((asset) => (
        <MarkButton key={asset.id} assetId={asset.id} label={asset.label} onPick={() => sign(asset.id)} />
      ))}
      <output className="readout">{status}</output>
    </div>
  );
}

export default function App() {
  return (
    <Viewer engine={engine} plugins={plugins} initialDocuments={[{ source: ebook }]}>
      <DocumentGate fallback={<p className="loading">Loading…</p>}>
        <SignBar />
        <Stage className="stage">
          {() => (
            <>
              <RenderLayer />
              {/* An empty signature field is "sign here": a click makes it the target */}
              <FormLayer />
            </>
          )}
        </Stage>
      </DocumentGate>
    </Viewer>
  );
}
```

**`basic.css`**

```css
/* Colors */
:root {
  --ink: #1a2748;
  --muted: #5a6b92;
  --line: #e6eaf2;
  --line-strong: #dce8fc;
  --surface: #ffffff;
  --tint: #f3f7fe;
  --canvas: #f7f9fc;
  --focus: #7db6ff;
  --shadow: rgb(7 32 76 / 0.04);
}

/* The controls, above the pages */
.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font: inherit;
  font-size: 13px;
  font-weight: 550;
  line-height: 1;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 8px 13px;
  cursor: pointer;
  white-space: nowrap;
  box-shadow: 0 1px 2px var(--shadow);
  transition:
    background-color 0.15s ease,
    border-color 0.15s ease;
}

.button:hover {
  background: var(--tint);
  border-color: var(--line-strong);
}

.button:active {
  transform: translateY(1px);
}

.button:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
}

.readout {
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}

/* A mark's picture, inside its button */
.preview {
  display: block;
  height: 22px;
}

/* The pages */
.stage {
  height: 440px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--canvas);
  box-shadow:
    0 1px 2px var(--shadow),
    0 18px 40px -28px rgb(7 32 76 / 0.28);
}

.loading {
  margin: 0;
  padding: 24px 0;
  text-align: center;
  font-size: 13px;
  color: var(--muted);
}
```

**`signature-plugin.ts`**

```typescript
import { formPlugin } from '@embedpdf/react/form';
import { indexedDbKeyStore, personalSigner, signaturePlugin } from '@embedpdf/react/signature';
import { stampPlugin } from '@embedpdf/react/stamp';
import { rootCertificate } from './certificates';

export const plugins = [
  /* … */
  formPlugin(),
  stampPlugin(),
  signaturePlugin({
    key: () => personalSigner({ subject: 'Ada Lovelace', store: indexedDbKeyStore('my-app-keys') }),
    trust: { anchors: async () => [rootCertificate] }, // the certificates you trust
  }),
];
```

## Sign a field

```ts
const { version } = await signature.sign({
  field: toFieldRef('approval'),
  mark: { assetId },
  signer: { reason: 'Approved', location: 'Amsterdam' },
});
```

The mark becomes what the field shows, the key seals the document, and the signed document is saved
as a new version. If anything fails along the way, nothing is left half-signed.

A mark is a stamp from a person's signature library, or image bytes you bring:

```ts
{ assetId } // a stamp, drawn, typed or uploaded; see "A person's signatures" below
{ source: pngBytes } // a PNG, a JPEG, or a one-page PDF
```

## Let people click to sign

People can also arm their signature and click where it goes, as in Preview. With the stamp plugin, arm
a mark from a signature library:

- **over an empty signature field**, the click signs it;
- **over a signed field**, nothing happens;
- **anywhere else**, the mark is placed as a stamp.

`placeMark()` does the same from code:

```ts
await signature.placeMark({ assetId }, { field: toFieldRef('approval') }); // signs the field
await signature.placeMark({ assetId }, { page: page.ref, center: { x: 120, y: 90 } }); // a stamp
```

What happens in a field depends on `mode`: `'sign'` signs it, `'visual'` only draws the mark in,
and `'ask'` asks your UI first through `onSignRequested`, so you can show your own sign dialog.

**`click-to-sign.tsx`**

```tsx
import { useEffect, useRef } from 'react';
import { Viewer, DocumentGate, usePageList } from '@embedpdf/react/runtime';
import type { OpenInput } from '@embedpdf/react/runtime';
import { Stage, stagePlugin, useStage } from '@embedpdf/react/stage';
import { RenderLayer, renderPlugin } from '@embedpdf/react/render';
import { interactionPlugin } from '@embedpdf/react/interaction';
import { AnnotationLayer, annotationPlugin } from '@embedpdf/react/annotation';
import { FormLayer, formPlugin, useForm, useFormState } from '@embedpdf/react/form';
import { stampPlugin, useStamp, useStampState } from '@embedpdf/react/stamp';
import {
  createTestSigner,
  signaturePlugin,
  useSignatureState,
  useSignerRows,
} from '@embedpdf/react/signature';
import { localEngine } from '@embedpdf/engine';

import './click-to-sign.css';

const engine = localEngine();
const assetEngine = engine; // a person's marks are stamps, kept as PDFs; they open here too
const signer = createTestSigner({ commonName: 'Ada Lovelace' });
const plugins = [
  stagePlugin(),
  renderPlugin(),
  interactionPlugin(),
  annotationPlugin(),
  formPlugin(),
  stampPlugin({ assetEngine }),
  signaturePlugin({ key: () => signer }),
];

const ebook = async (): Promise<OpenInput> => {
  const response = await fetch('https://snippet.embedpdf.com/ebook.pdf');
  return { kind: 'bytes', id: 'ebook', bytes: new Uint8Array(await response.arrayBuffer()) };
};

/** On load: a signature field on the last page, and a person's signature, armed. */
function useSetUp() {
  const form = useForm();
  const stamp = useStamp();
  const stage = useStage();
  const status = useFormState((state) => state.status);
  const page = usePageList().at(-1)?.ref;
  const done = useRef(false);

  useEffect(() => {
    if (status !== 'ready' || !page || done.current) return;
    done.current = true;
    void (async () => {
      await form.create({
        family: 'signature',
        name: 'approval',
        widgets: [{ page, rect: { x: 72, y: 560, width: 220, height: 64 }, color: '#94a3b8' }],
      });
      stage.goToPage(page);
      const { library } = await stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
      const { asset } = await stamp.createAsset({
        libraryId: library.id,
        name: 'signature',
        label: 'Signature',
        mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
      });
      await stamp.armAsset(asset.id, { targetWidth: 160 });
    })();
  }, [form, stamp, stage, status, page]);
}

function ArmBar() {
  useSetUp();
  const stamp = useStamp();
  const [person] = useSignerRows();
  const { armedAsset } = useStampState();
  const { signatures } = useSignatureState();
  const mark = person?.signatures[0];

  let hint = 'Getting ready…';
  if (signatures[0]) hint = `The field is signed by ${signatures[0].signer.name}`;
  else if (armedAsset) hint = 'Click the empty field to sign it, or anywhere else to place it';
  else if (mark) hint = 'Arm the signature, then click where it goes';

  return (
    <div className="toolbar">
      <button
        type="button"
        className="button"
        disabled={!mark}
        aria-pressed={armedAsset !== null}
        onClick={() => (armedAsset ? stamp.disarm() : mark && void stamp.armAsset(mark.id))}
      >
        {armedAsset ? 'Disarm' : 'Arm the signature'}
      </button>
      <output className="readout">{hint}</output>
    </div>
  );
}

export default function App() {
  return (
    <Viewer engine={engine} plugins={plugins} initialDocuments={[{ source: ebook }]}>
      <DocumentGate fallback={<p className="loading">Loading…</p>}>
        <ArmBar />
        <Stage className="stage">
          {() => (
            <>
              <RenderLayer />
              <AnnotationLayer />
              <FormLayer />
            </>
          )}
        </Stage>
      </DocumentGate>
    </Viewer>
  );
}
```

**`click-to-sign.css`**

```css
/* Colors */
:root {
  --ink: #1a2748;
  --muted: #5a6b92;
  --line: #e6eaf2;
  --line-strong: #dce8fc;
  --surface: #ffffff;
  --tint: #f3f7fe;
  --canvas: #f7f9fc;
  --accent: #054fb3;
  --focus: #7db6ff;
  --shadow: rgb(7 32 76 / 0.04);
}

/* The controls, above the pages */
.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
}

.button {
  font: inherit;
  font-size: 13px;
  font-weight: 550;
  line-height: 1;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 8px 13px;
  cursor: pointer;
  white-space: nowrap;
  box-shadow: 0 1px 2px var(--shadow);
  transition:
    background-color 0.15s ease,
    border-color 0.15s ease;
}

.button:hover {
  background: var(--tint);
  border-color: var(--line-strong);
}

.button:active {
  transform: translateY(1px);
}

.button:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
}

.button[aria-pressed='true'] {
  color: var(--accent);
  background: var(--tint);
  border-color: var(--line-strong);
}

.readout {
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}

/* The pages */
.stage {
  height: 440px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--canvas);
  box-shadow:
    0 1px 2px var(--shadow),
    0 18px 40px -28px rgb(7 32 76 / 0.28);
}

.loading {
  margin: 0;
  padding: 24px 0;
  text-align: center;
  font-size: 13px;
  color: var(--muted);
}
```

## Fill a field without signing

Sometimes a signature only needs to look signed, such as for a form that gets printed. Draw the mark
into the field without sealing anything:

```ts
await signature.fillField(toFieldRef('approval'), { source: pngBytes });
await signature.clearField(toFieldRef('approval'));
```

A signed field can't be filled or cleared: what it shows is part of what was signed.

**`fill.tsx`**

```tsx
import { useEffect, useRef, useState } from 'react';
import { Viewer, DocumentGate, usePageList } from '@embedpdf/react/runtime';
import type { OpenInput } from '@embedpdf/react/runtime';
import { Stage, stagePlugin, useStage } from '@embedpdf/react/stage';
import { RenderLayer, renderPlugin } from '@embedpdf/react/render';
import { interactionPlugin } from '@embedpdf/react/interaction';
import { formPlugin, toFieldRef, useForm, useFormState } from '@embedpdf/react/form';
import { stampPlugin, useStamp } from '@embedpdf/react/stamp';
import { signaturePlugin, useSignature, useSignatureEvent } from '@embedpdf/react/signature';
import { localEngine } from '@embedpdf/engine';

import './fill.css';

const engine = localEngine();
const assetEngine = engine; // a person's marks are stamps, kept as PDFs; they open here too
// No key: a mark is only drawn in, nothing is sealed.
const plugins = [
  stagePlugin(),
  renderPlugin(),
  interactionPlugin(),
  formPlugin(),
  stampPlugin({ assetEngine }),
  signaturePlugin(),
];

const ebook = async (): Promise<OpenInput> => {
  const response = await fetch('https://snippet.embedpdf.com/ebook.pdf');
  return { kind: 'bytes', id: 'ebook', bytes: new Uint8Array(await response.arrayBuffer()) };
};

const APPROVAL = toFieldRef('approval');

function FillBar() {
  const form = useForm();
  const stamp = useStamp();
  const stage = useStage();
  const signature = useSignature();
  const status = useFormState((state) => state.status);
  const page = usePageList().at(-1)?.ref;
  const [assetId, setAssetId] = useState<string | null>(null);
  const [drawn, setDrawn] = useState(false);
  const done = useRef(false);

  useSignatureEvent((plugin) => plugin.onFilled, () => setDrawn(true));
  useSignatureEvent((plugin) => plugin.onCleared, () => setDrawn(false));

  // On load: a signature field on the last page, a typed signature, drawn into the field.
  useEffect(() => {
    if (status !== 'ready' || !page || done.current) return;
    done.current = true;
    void (async () => {
      await form.create({
        family: 'signature',
        name: 'approval',
        widgets: [{ page, rect: { x: 72, y: 560, width: 220, height: 64 }, color: '#94a3b8' }],
      });
      stage.goToPage(page);
      const { library } = await stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
      const { asset } = await stamp.createAsset({
        libraryId: library.id,
        name: 'signature',
        label: 'Signature',
        mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
      });
      setAssetId(asset.id);
      await signature.fillField(APPROVAL, { assetId: asset.id });
    })();
  }, [form, stamp, stage, signature, status, page]);

  return (
    <div className="toolbar">
      <button
        type="button"
        className="button"
        disabled={!assetId || drawn}
        onClick={() => assetId && void signature.fillField(APPROVAL, { assetId })}
      >
        Draw it in
      </button>
      <button
        type="button"
        className="button"
        disabled={!drawn}
        onClick={() => void signature.clearField(APPROVAL)}
      >
        Take it out
      </button>
      <output className="readout">
        {drawn ? 'Drawn in, not signed: no key sealed anything' : 'The field is empty'}
      </output>
    </div>
  );
}

export default function App() {
  return (
    <Viewer engine={engine} plugins={plugins} initialDocuments={[{ source: ebook }]}>
      <DocumentGate fallback={<p className="loading">Loading…</p>}>
        <FillBar />
        <Stage className="stage">{() => <RenderLayer />}</Stage>
      </DocumentGate>
    </Viewer>
  );
}
```

**`fill.css`**

```css
/* Colors */
:root {
  --ink: #1a2748;
  --muted: #5a6b92;
  --line: #e6eaf2;
  --line-strong: #dce8fc;
  --surface: #ffffff;
  --tint: #f3f7fe;
  --canvas: #f7f9fc;
  --focus: #7db6ff;
  --shadow: rgb(7 32 76 / 0.04);
}

/* The controls, above the pages */
.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
}

.button {
  font: inherit;
  font-size: 13px;
  font-weight: 550;
  line-height: 1;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 8px 13px;
  cursor: pointer;
  white-space: nowrap;
  box-shadow: 0 1px 2px var(--shadow);
  transition:
    background-color 0.15s ease,
    border-color 0.15s ease;
}

.button:hover {
  background: var(--tint);
  border-color: var(--line-strong);
}

.button:active {
  transform: translateY(1px);
}

.button:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
}

.readout {
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}

/* The pages */
.stage {
  height: 440px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--canvas);
  box-shadow:
    0 1px 2px var(--shadow),
    0 18px 40px -28px rgb(7 32 76 / 0.28);
}

.loading {
  margin: 0;
  padding: 24px 0;
  text-align: center;
  font-size: 13px;
  color: var(--muted);
}
```

## The key

The engine never holds a key. You give the plugin a **signer**, which does the signing.
`@embedpdf/react/signature` has one for each case:

```ts
// Your own key and certificate chain
webCryptoSigner({ privateKey, certificateChain: [leaf, issuer] });

// Your signing service or hardware module: only the document's fingerprint leaves the browser
remoteSigner({ sign: ({ digest, algorithm, subFilter }) => api.sign(digest, algorithm, subFilter) });

// A key per person, created in the browser and kept there, never readable
personalSigner({ subject: 'Ada Lovelace', store: indexedDbKeyStore('my-app-keys') });

// For tests and demos
createTestSigner({ commonName: 'Demo' });
```

A personal signer works like signing in Preview, with real cryptography: a reader who trusts that
person's certificate sees a valid signature, and everyone else sees "validity unknown", the honest
answer for a key the person made themselves. For signatures everyone can check, sign with a
certificate from a trusted provider, through `webCryptoSigner` or `remoteSigner`.

### Signing in two steps

When the key signs somewhere else, such as on a phone or in a signing service that asks for approval,
split the signing in two:

```ts
const { signingId, digest } = await signature.prepareSignature({ field, mark: { assetId } });
const cms = await myService.sign(digest); // may take minutes
await signature.completeSignature(signingId, cms);
```

While a signature is prepared, the document can't be changed, so nothing can slip in between.
`signature.cancelPending()` gives up.

## Check the signatures

**`signature-list.tsx`**

```tsx
import { useSignatureState } from '@embedpdf/react/signature';

export function SignatureList() {
  const { signatures } = useSignatureState();

  return (
    <ul>
      {signatures.map((sig) => (
        <li key={sig.fieldName}>
          {sig.fieldName}: {sig.verdict?.summary ?? 'checking…'}
        </li>
      ))}
    </ul>
  );
}
```

A verdict's `summary` is:

| Summary             | Means                                                                |
| :------------------ | :------------------------------------------------------------------- |
| `'valid'`           | Nothing changed since it was signed, and you trust the signer        |
| `'valid-untrusted'` | Nothing changed, but the signer's certificate isn't one you trust    |
| `'invalid'`         | The document changed in a way the signature doesn't allow            |
| `'indeterminate'`   | It couldn't be checked, for example because a certificate is missing |

The plugin checks the signatures when the document opens, and again after every change. For a
detailed report of what changed since a signature, rule by rule, use `signature.analyzeChanges()`.

## Warn before an edit breaks a signature

After an approval signature, filling in the form and adding more signatures keep it valid, but an
annotation doesn't. The plugin warns you the moment a change would break a signature once it's saved,
as Acrobat does:

**`break-warning.tsx`**

```tsx
import { useSignature, useSignatureEvent } from '@embedpdf/react/signature';
import { toast } from './toast';

export function SignatureGuard() {
  const signature = useSignature();

  useSignatureEvent(
    (s) => s.onInvalidationPredicted,
    ({ field }) => {
      const name = signature.getSignature(field)?.fieldName;
      toast(`This change will break the signature in "${name}" when saved.`);
    },
  );

  return null;
}
```

`signature.getProtection()` tells you what the document's signatures allow, before anyone tries. A
signer who wants comments to stay allowed signs with a certification that allows them.

**`break-warning.tsx`**

```tsx
import { useEffect, useRef, useState } from 'react';
import { Viewer, DocumentGate, usePageList } from '@embedpdf/react/runtime';
import type { OpenInput } from '@embedpdf/react/runtime';
import { Stage, stagePlugin, useStage } from '@embedpdf/react/stage';
import { RenderLayer, renderPlugin } from '@embedpdf/react/render';
import { interactionPlugin } from '@embedpdf/react/interaction';
import { AnnotationLayer, annotationPlugin, useAnnotation } from '@embedpdf/react/annotation';
import { formPlugin, toFieldRef, useForm, useFormState } from '@embedpdf/react/form';
import { stampPlugin, useStamp } from '@embedpdf/react/stamp';
import {
  createTestSigner,
  signaturePlugin,
  useSignature,
  useSignatureEvent,
  useSignatureState,
} from '@embedpdf/react/signature';
import { localEngine } from '@embedpdf/engine';

import './break-warning.css';

const engine = localEngine();
const assetEngine = engine; // a person's marks are stamps, kept as PDFs; they open here too
const signer = createTestSigner({ commonName: 'Ada Lovelace' });
const plugins = [
  stagePlugin(),
  renderPlugin(),
  interactionPlugin(),
  annotationPlugin(),
  formPlugin(),
  stampPlugin({ assetEngine }),
  signaturePlugin({
    key: () => signer,
    // Trust the demo key itself, so its signature checks out as 'valid'.
    trust: { anchors: async () => [(await signer).certificate] },
  }),
];

const ebook = async (): Promise<OpenInput> => {
  const response = await fetch('https://snippet.embedpdf.com/ebook.pdf');
  return { kind: 'bytes', id: 'ebook', bytes: new Uint8Array(await response.arrayBuffer()) };
};

/** On load: a signature field on the last page, signed by Ada with a typed signature. */
function useSignedDocument() {
  const form = useForm();
  const stamp = useStamp();
  const stage = useStage();
  const signature = useSignature();
  const status = useFormState((state) => state.status);
  const page = usePageList().at(-1)?.ref;
  const done = useRef(false);

  useEffect(() => {
    if (status !== 'ready' || !page || done.current) return;
    done.current = true;
    void (async () => {
      await form.create({
        family: 'signature',
        name: 'approval',
        widgets: [{ page, rect: { x: 72, y: 560, width: 220, height: 64 } }],
      });
      stage.goToPage(page);
      const { library } = await stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
      const { asset } = await stamp.createAsset({
        libraryId: library.id,
        name: 'signature',
        label: 'Signature',
        mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
      });
      await signature.sign({ field: toFieldRef('approval'), mark: { assetId: asset.id } });
    })();
  }, [form, stamp, stage, signature, status, page]);
}

function WarningBar() {
  useSignedDocument();
  const annotation = useAnnotation();
  const signature = useSignature();
  const page = usePageList().at(-1)?.ref;
  const { signatures } = useSignatureState();
  const [warning, setWarning] = useState<string | null>(null);
  const signed = signatures[0];

  // The moment a change would break a signature once it's saved, as Acrobat warns.
  useSignatureEvent(
    (plugin) => plugin.onInvalidationPredicted,
    ({ field }) => {
      const name = signature.getSignature(field)?.fieldName;
      setWarning(`This change will break the signature in "${name}" when saved.`);
    },
  );

  return (
    <div className="toolbar">
      <button
        type="button"
        className="button"
        disabled={!signed || !page}
        onClick={() =>
          page &&
          void annotation.create(page, {
            subtype: 'square',
            box: { x: 320, y: 560, width: 140, height: 64 },
            color: '#e11d48',
            strokeWidth: 2,
          })
        }
      >
        Draw a box on the page
      </button>
      <output className="readout">
        {signed ? `Signed by ${signed.signer.name}: ${signed.verdict?.summary ?? 'checking…'}` : 'Signing…'}
      </output>
      {warning && <output className="warning">{warning}</output>}
    </div>
  );
}

export default function App() {
  return (
    <Viewer engine={engine} plugins={plugins} initialDocuments={[{ source: ebook }]}>
      <DocumentGate fallback={<p className="loading">Loading…</p>}>
        <WarningBar />
        <Stage className="stage">
          {() => (
            <>
              <RenderLayer />
              <AnnotationLayer />
            </>
          )}
        </Stage>
      </DocumentGate>
    </Viewer>
  );
}
```

**`break-warning.css`**

```css
/* Colors */
:root {
  --ink: #1a2748;
  --muted: #5a6b92;
  --line: #e6eaf2;
  --line-strong: #dce8fc;
  --surface: #ffffff;
  --tint: #f3f7fe;
  --canvas: #f7f9fc;
  --warn: #b45309;
  --warn-tint: #fffbeb;
  --focus: #7db6ff;
  --shadow: rgb(7 32 76 / 0.04);
}

/* The controls, above the pages */
.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-bottom: 14px;
}

.button {
  font: inherit;
  font-size: 13px;
  font-weight: 550;
  line-height: 1;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 8px 13px;
  cursor: pointer;
  white-space: nowrap;
  box-shadow: 0 1px 2px var(--shadow);
  transition:
    background-color 0.15s ease,
    border-color 0.15s ease;
}

.button:hover {
  background: var(--tint);
  border-color: var(--line-strong);
}

.button:active {
  transform: translateY(1px);
}

.button:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
}

.readout {
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}

.warning {
  flex: 1 1 100%;
  font-size: 13px;
  color: var(--warn);
  background: var(--warn-tint);
  border: 1px solid #fde68a;
  border-radius: 9px;
  padding: 8px 12px;
}

/* The pages */
.stage {
  height: 440px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--canvas);
  box-shadow:
    0 1px 2px var(--shadow),
    0 18px 40px -28px rgb(7 32 76 / 0.28);
}

.loading {
  margin: 0;
  padding: 24px 0;
  text-align: center;
  font-size: 13px;
  color: var(--muted);
}
```

## A person's signatures

A person's signature and initials are stamps, in a library of kind `'signatures'`, drawn, typed or
uploaded with the [stamp plugin](../annotations/stamps):

```ts
const { library } = await stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
await stamp.createAsset({ libraryId: library.id, name: 'signature', label: 'Signature', mark: { kind: 'ink', strokes } });
await stamp.createAsset({
  libraryId: library.id,
  name: 'initials',
  label: 'Initials',
  mark: { kind: 'text', text: 'AL', fontFamily: 'times-italic' },
});
```

`useSignerRows()` lists each person with their signature and initials, for a picker. The library is
a normal PDF, so Acrobat can open it too.

## "Sign here" in a form

With the [form layer](../forms), an empty signature field shows a "sign here" button. Clicking it makes
the field the **target**: the next mark the person picks goes there. A signed field, clicked, asks your
UI to show its details:

```ts
signature.setTarget(toFieldRef('approval')); // the next mark goes here; null clears
```

| Event                   | Fires when                                     | Show                    |
| :---------------------- | :--------------------------------------------- | :---------------------- |
| `onTargetChanged`       | A field became the target                      | your signatures panel   |
| `onSignRequested`       | In `'ask'` mode, a mark was dropped on a field | your sign dialog        |
| `onInspectionRequested` | A signed field was clicked                     | the signature's details |

## Methods

Everything `useSignature()` gives you.

| Method                                                                   | What it does                                                                                                                                                                                                                                                      |
| :----------------------------------------------------------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `sign({ field, mark })`                                                  | Signs a field: the mark becomes what it shows, and the key seals the document. Also takes `signer`, a per-call `key`, `certify` and `lock`, and resolves `{ signature, version, protection }`. [Sign a field](#sign-a-field)                                      |
| `placeMark(mark, { field })`, `placeMark(mark, { page, center })`        | Does what a click with an armed mark does: in a field, signs, fills or asks, by `mode`; anywhere else, places a stamp. Resolves what it did as `kind`: `'signed'`, `'filled'`, `'requested'` or `'placed'`. [Let people click to sign](#let-people-click-to-sign) |
| `fillField(field, mark)`, `clearField(field)`                            | Draws a mark into a field without signing, or takes it out again. Refused on a signed field. [Fill a field without signing](#fill-a-field-without-signing)                                                                                                        |
| `prepareSignature({ field, mark })`, `completeSignature(signingId, cms)` | Signs in two steps: the first resolves `{ signingId, digest }` for your key to sign, the second seals the document with what the key returned. [Signing in two steps](#signing-in-two-steps)                                                                      |
| `cancelPending()`                                                        | Gives up a signature prepared in two steps, so the document can be changed again                                                                                                                                                                                  |
| `validate({ until? })`                                                   | Checks every signature again and resolves the verdicts. `until: 'persisted'` checks the file as it was opened. [Which bytes are checked](#which-bytes-are-checked)                                                                                                |
| `validateField(field)`                                                   | Checks one signed field and resolves its verdict                                                                                                                                                                                                                  |
| `getVerdict(field)`, `listVerdicts()`                                    | One signed field's verdict from the last check, or every verdict; `null` before the first check. [Check the signatures](#check-the-signatures)                                                                                                                    |
| `getSignature(field)`                                                    | One signature field's facts, signed or not, such as `fieldName`, `signed` and `signer`, or `null`                                                                                                                                                                 |
| `listUnsignedFields()`                                                   | The signature fields still to sign, in document order                                                                                                                                                                                                             |
| `analyzeChanges({ since })`                                              | What changed after a signature (`{ signatureIndex }`) or a version of the file (`{ revisionIndex }`), rule by rule                                                                                                                                                |
| `readRevision(field)`, `readRevision({ revisionIndex })`                 | The exact bytes of the file version a signature covers. [The signed bytes](#the-signed-bytes)                                                                                                                                                                     |
| `setTarget(field)`                                                       | Makes a field the target, where the next mark the person picks goes; `null` clears. ["Sign here" in a form](#sign-here-in-a-form)                                                                                                                                 |
| `requestInspection(field)`                                               | Asks your UI to show a signed field's details, as clicking it does: `onInspectionRequested` fires                                                                                                                                                                 |
| `getMode()`                                                              | The mode in effect: the `mode` setting, or its default. [Settings](#settings)                                                                                                                                                                                     |
| `getSnapshot()`                                                          | Everything at once, as the engine reads it: every signature field, signed or not, the file's versions, and `protection`                                                                                                                                           |
| `refresh()`                                                              | Reads the signatures again. You rarely need it: the plugin reads and checks them again after every change.                                                                                                                                                        |
| `canSign(field)`, `canCertify()`, `canFill(field)`, `canReadRevision()`  | Whether signing a field, certifying, drawing a mark into a field without signing, and reading the signed bytes are allowed. [Permissions](#permissions)                                                                                                           |
| `getSettings()`, `updateSettings(changes)`, `resetSettings()`            | Reads the settings, changes them while the app runs, or goes back to what you registered. In a component, use `useSignatureSettings()`. [Settings](#settings)                                                                                                     |

`field` is a field's ref, such as `toFieldRef('approval')`; the methods that only read also take the
ref of the field's box. Every method that returns a promise also takes a `signal` in its options, to
cancel it.

## State

Everything `useSignatureState()` gives you. Your component re-renders when a value changes. The method in the last column reads the same value once.

| Field        | What it is                                                                                                                                                       | Read once          |
| :----------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------- | :----------------- |
| `signatures` | The signed fields, in document order, each with its `verdict` once checked                                                                                       | `listSignatures()` |
| `protection` | What the document's signatures allow, or `null` before they're read                                                                                              | `getProtection()`  |
| `target`     | The field the next mark goes to, or `null`                                                                                                                       | `getTarget()`      |
| `busy`       | Whether a signing or a fill is running                                                                                                                           | `isBusy()`         |
| `pending`    | A signature prepared in two steps and not completed yet, as `{ signingId, field }`, or `null`. Until it's completed or cancelled, the document can't be changed. | `getPending()`     |
| `status`     | Whether the signatures are read: `'idle'`, `'loading'`, `'ready'`, `'forbidden'` or `'error'`                                                                    | `getStatus()`      |

## Settings

Set them when you register the plugin, and change them while the app runs with
`signature.updateSettings({ … })`; `signature.resetSettings()` goes back to what you registered, and
`useSignatureSettings()` gives you the current settings.

| Setting        | What it does                                                            | Default                              |
| :------------- | :---------------------------------------------------------------------- | :----------------------------------- |
| `key`          | The signer, or a function that returns one when someone signs           | none                                 |
| `mode`         | What a mark does in a field: `'sign'`, `'visual'` or `'ask'`            | `'sign'` with a key, else `'visual'` |
| `trust`        | The certificates you trust, for checking signatures                     | none                                 |
| `allowCertify` | Let a first signature be a certification, which sets what stays allowed | `false`                              |

## Events

**`save-warning.tsx`**

```tsx
import { useSignatureEvent } from '@embedpdf/react/signature';
import { showWarning } from './warnings';

export function SaveWarning() {
  useSignatureEvent(
    (signature) => signature.onInvalidationPredicted,
    () => showWarning('Saving this change will break a signature.'),
  );

  return null;
}
```

| Event                     | Fires when                                           | Carries                       |
| :------------------------ | :--------------------------------------------------- | :---------------------------- |
| `onSigned`                | A field was signed, whoever signed it                | `field`, `result`, `origin`   |
| `onFilled`, `onCleared`   | A mark was drawn into a field, or removed            | `field`                       |
| `onValidated`             | The signatures were checked                          | `verdicts`                    |
| `onProtectionChanged`     | What the signatures allow changed                    | `protection`                  |
| `onInvalidationPredicted` | A change would break a signature once saved          | `field`, `detail`             |
| `onTargetChanged`         | A field became the target, or the target was cleared | `field` (`null` when cleared) |
| `onSignRequested`         | In `'ask'` mode, a mark was dropped on a field       | `field`, `mark`               |
| `onInspectionRequested`   | A signed field was clicked                           | `field`                       |
| `onSettingsChanged`       | The settings changed                                 | `settings`, `changed`         |

`result` is what `sign()` resolves. ["Sign here" in a form](#sign-here-in-a-form) says what to show
for the last three.

## Permissions

| Permission         | What it allows                              | Check                         |
| :----------------- | :------------------------------------------ | :---------------------------- |
| `doc.sign`         | Signing                                     | `signature.canSign(field)`    |
| `doc.sign.certify` | Signing a certification                     | `signature.canCertify()`      |
| `doc.forms.fill`   | Drawing a mark into a field without signing | `signature.canFill(field)`    |
| `doc.download`     | Reading the exact bytes a signature covers  | `signature.canReadRevision()` |

A user with a `fields:sign` (`fields:fill`) permission for one group signs (fills in) that group's
fields only, so the checks take the field. See [Signers and groups](https://www.embedpdf.com/docs/engine/forms/groups). On a
signed document, the engine also refuses what its signatures forbid.

## Good to know

### Which bytes are checked

The plugin checks the document as it is in the viewer, with changes that haven't been downloaded yet,
so the verdict is the one the downloaded file will get. `validate({ until: 'persisted' })` checks the
file as it was opened.

### The signed bytes

`signature.readRevision({ revisionIndex })` gives you the exact version of the file a signature
covers, for an audit trail.

> How signatures are stored, and what each certification allows, is on
> [Digital signatures](https://www.embedpdf.com/docs/engine/forms/signatures).