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.

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import {
  ChangeDetectionStrategy,
  Component,
  computed,
  effect,
  inject,
  input,
  output,
  signal,
  untracked,
  viewChild,
  ViewEncapsulation,
} from '@angular/core';
import { EpdfDocument, EpdfDocumentGate, provideEmbedPdf } from '@embedpdf/angular/runtime';
import type { OpenInput, PageRef } from '@embedpdf/angular/runtime';
import { EpdfPageTemplate, EpdfStage, withStage } from '@embedpdf/angular/stage';
import { EpdfRenderLayer, withRender } from '@embedpdf/angular/render';
import { withInteraction } from '@embedpdf/angular/interaction';
import { EpdfForm, EpdfFormLayer, withForm } from '@embedpdf/angular/form';
import { EpdfStamp, withStamp } from '@embedpdf/angular/stamp';
import { createTestSigner, EpdfSignature, withSignature } from '@embedpdf/angular/signature';
import { localEngine } from '@embedpdf/engine';

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 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()) };
};

// A mark's button: its picture once there is one, its label until then.
@Component({
  selector: 'button[demoMarkButton]',
  changeDetection: ChangeDetectionStrategy.OnPush,
  host: { type: 'button', class: 'button', '[title]': 'label()', '(click)': 'pick.emit()' },
  template: `
    @if (url(); as url) {
      <img [src]="url" [alt]="label()" class="preview" />
    } @else {
      {{ label() }}
    }
  `,
})
export class MarkButton {
  readonly assetId = input.required<string>();
  readonly label = input.required<string>();
  readonly pick = output();
  protected readonly url = inject(EpdfStamp).previewUrlOf(() => this.assetId());
}

@Component({
  selector: 'demo-root',
  imports: [
    EpdfDocumentGate,
    EpdfStage,
    EpdfPageTemplate,
    EpdfRenderLayer,
    EpdfFormLayer,
    MarkButton,
  ],
  providers: [
    provideEmbedPdf(
      { engine, initialDocuments: [{ source: ebook }] },
      withStage(),
      withRender(),
      withInteraction(),
      withForm(),
      withStamp({ assetEngine }),
      withSignature({
        key: () => signer,
        // Trust the demo key itself, so its signatures check out as 'valid'.
        trust: { anchors: async () => [(await signer).certificate] },
      }),
    ),
  ],
  changeDetection: ChangeDetectionStrategy.OnPush,
  styleUrl: './basic.css',
  encapsulation: ViewEncapsulation.None,
  template: `
    <ng-container *epdfDocumentGate="let document; fallback: loading">
      <div class="toolbar">
        @for (asset of person()?.signatures; track asset.id) {
          <button demoMarkButton [assetId]="asset.id" [label]="asset.label" (pick)="sign(asset.id)"></button>
        }
        <output class="readout">{{ status() }}</output>
      </div>
      <epdf-stage class="stage">
        <ng-template epdfPage>
          <epdf-render-layer />
          <!-- An empty signature field is "sign here": a click makes it the target -->
          <epdf-form-layer />
        </ng-template>
      </epdf-stage>
    </ng-container>

    <ng-template #loading><p class="loading">Loading…</p></ng-template>
  `,
})
export class App {
  private readonly form = inject(EpdfForm);
  private readonly stamp = inject(EpdfStamp);
  private readonly signature = inject(EpdfSignature);
  private readonly document = inject(EpdfDocument);
  private readonly stage = viewChild(EpdfStage);
  private done = false;

  protected readonly person = computed(() => this.signature.signerRows()[0]);
  private readonly field = computed(() =>
    this.form.fields().find((candidate) => candidate.family === 'signature'),
  );
  private readonly error = signal<string | null>(null);

  protected readonly status = computed(() => {
    const signed = this.signature.signatures()[0];
    const error = this.error();
    if (!this.person() || !this.field()) return 'Getting ready…';
    if (error) return error;
    if (this.signature.busy()) return 'Signing…';
    if (signed) return `Signed by ${signed.signer.name}: ${signed.verdict?.summary ?? 'checking…'}`;
    if (this.signature.target()) return 'Now pick the signature';
    return 'Click the field, or pick the signature';
  });

  constructor() {
    // 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.
    effect(() => {
      const page = this.document.pages().at(-1)?.ref;
      const stage = this.stage();
      if (this.form.status() !== 'ready' || !page || !stage || this.done) return;
      this.done = true;
      untracked(() => void this.setUp(page, stage));
    });
  }

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

  private async setUp(page: PageRef, stage: EpdfStage) {
    await this.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 this.stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
    await this.stamp.createAsset({
      libraryId: library.id,
      name: 'signature',
      label: 'Signature',
      mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
    });
  }
}

signature-plugin.ts

import { Component } from '@angular/core';
import { withForm } from '@embedpdf/angular/form';
import { provideEmbedPdf } from '@embedpdf/angular/runtime';
import { indexedDbKeyStore, personalSigner, withSignature } from '@embedpdf/angular/signature';
import { withStamp } from '@embedpdf/angular/stamp';
import { rootCertificate } from './certificates';
import { engine } from './pdf';

@Component({
  selector: 'app-signing',
  providers: [
    provideEmbedPdf(
      { engine },
      /* … */
      withForm(),
      withStamp(),
      withSignature({
        key: () => personalSigner({ subject: 'Ada Lovelace', store: indexedDbKeyStore('my-app-keys') }),
        trust: { anchors: async () => [rootCertificate] }, // the certificates you trust
      }),
    ),
  ],
  template: `<!-- … -->`,
})
export class Signing {}

Sign a field#

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:

{ 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:

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 signRequested$, so you can show your own sign dialog.

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import {
  ChangeDetectionStrategy,
  Component,
  computed,
  effect,
  inject,
  untracked,
  viewChild,
  ViewEncapsulation,
} from '@angular/core';
import { EpdfDocument, EpdfDocumentGate, provideEmbedPdf } from '@embedpdf/angular/runtime';
import type { OpenInput, PageRef } from '@embedpdf/angular/runtime';
import { EpdfPageTemplate, EpdfStage, withStage } from '@embedpdf/angular/stage';
import { EpdfRenderLayer, withRender } from '@embedpdf/angular/render';
import { withInteraction } from '@embedpdf/angular/interaction';
import { EpdfAnnotationLayer, withAnnotation } from '@embedpdf/angular/annotation';
import { EpdfForm, EpdfFormLayer, withForm } from '@embedpdf/angular/form';
import { EpdfStamp, withStamp } from '@embedpdf/angular/stamp';
import { createTestSigner, EpdfSignature, withSignature } from '@embedpdf/angular/signature';
import { localEngine } from '@embedpdf/engine';

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 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()) };
};

@Component({
  selector: 'demo-root',
  imports: [
    EpdfDocumentGate,
    EpdfStage,
    EpdfPageTemplate,
    EpdfRenderLayer,
    EpdfAnnotationLayer,
    EpdfFormLayer,
  ],
  providers: [
    provideEmbedPdf(
      { engine, initialDocuments: [{ source: ebook }] },
      withStage(),
      withRender(),
      withInteraction(),
      withAnnotation(),
      withForm(),
      withStamp({ assetEngine }),
      withSignature({ key: () => signer }),
    ),
  ],
  changeDetection: ChangeDetectionStrategy.OnPush,
  styleUrl: './click-to-sign.css',
  encapsulation: ViewEncapsulation.None,
  template: `
    <ng-container *epdfDocumentGate="let document; fallback: loading">
      <div class="toolbar">
        <button
          type="button"
          class="button"
          [disabled]="!mark()"
          [attr.aria-pressed]="stamp.armedAsset() !== null"
          (click)="toggleArmed()"
        >
          {{ stamp.armedAsset() ? 'Disarm' : 'Arm the signature' }}
        </button>
        <output class="readout">{{ hint() }}</output>
      </div>
      <epdf-stage class="stage">
        <ng-template epdfPage>
          <epdf-render-layer />
          <epdf-annotation-layer />
          <epdf-form-layer />
        </ng-template>
      </epdf-stage>
    </ng-container>

    <ng-template #loading><p class="loading">Loading…</p></ng-template>
  `,
})
export class App {
  protected readonly stamp = inject(EpdfStamp);
  private readonly form = inject(EpdfForm);
  private readonly signature = inject(EpdfSignature);
  private readonly document = inject(EpdfDocument);
  private readonly stage = viewChild(EpdfStage);
  private done = false;

  protected readonly mark = computed(() => this.signature.signerRows()[0]?.signatures[0]);

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

  constructor() {
    // On load: a signature field on the last page, and a person's signature, armed.
    effect(() => {
      const page = this.document.pages().at(-1)?.ref;
      const stage = this.stage();
      if (this.form.status() !== 'ready' || !page || !stage || this.done) return;
      this.done = true;
      untracked(() => void this.setUp(page, stage));
    });
  }

  protected toggleArmed() {
    const mark = this.mark();
    if (this.stamp.armedAsset()) this.stamp.disarm();
    else if (mark) void this.stamp.armAsset(mark.id);
  }

  private async setUp(page: PageRef, stage: EpdfStage) {
    await this.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 this.stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
    const { asset } = await this.stamp.createAsset({
      libraryId: library.id,
      name: 'signature',
      label: 'Signature',
      mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
    });
    await this.stamp.armAsset(asset.id, { targetWidth: 160 });
  }
}

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:

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.

Loading live preview…

import {
  ChangeDetectionStrategy,
  Component,
  effect,
  inject,
  signal,
  untracked,
  viewChild,
  ViewEncapsulation,
} from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { EpdfDocument, EpdfDocumentGate, provideEmbedPdf } from '@embedpdf/angular/runtime';
import type { OpenInput, PageRef } from '@embedpdf/angular/runtime';
import { EpdfPageTemplate, EpdfStage, withStage } from '@embedpdf/angular/stage';
import { EpdfRenderLayer, withRender } from '@embedpdf/angular/render';
import { withInteraction } from '@embedpdf/angular/interaction';
import { EpdfForm, toFieldRef, withForm } from '@embedpdf/angular/form';
import { EpdfStamp, withStamp } from '@embedpdf/angular/stamp';
import { EpdfSignature, withSignature } from '@embedpdf/angular/signature';
import { localEngine } from '@embedpdf/engine';

const engine = localEngine();
const assetEngine = engine; // a person's marks are stamps, kept as PDFs; they open here too

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');

@Component({
  selector: 'demo-root',
  imports: [EpdfDocumentGate, EpdfStage, EpdfPageTemplate, EpdfRenderLayer],
  providers: [
    provideEmbedPdf(
      { engine, initialDocuments: [{ source: ebook }] },
      withStage(),
      withRender(),
      withInteraction(),
      withForm(),
      withStamp({ assetEngine }),
      // No key: a mark is only drawn in, nothing is sealed.
      withSignature(),
    ),
  ],
  changeDetection: ChangeDetectionStrategy.OnPush,
  styleUrl: './fill.css',
  encapsulation: ViewEncapsulation.None,
  template: `
    <ng-container *epdfDocumentGate="let document; fallback: loading">
      <div class="toolbar">
        <button type="button" class="button" [disabled]="!assetId() || drawn()" (click)="drawIn()">
          Draw it in
        </button>
        <button type="button" class="button" [disabled]="!drawn()" (click)="takeOut()">
          Take it out
        </button>
        <output class="readout">
          {{ drawn() ? 'Drawn in, not signed: no key sealed anything' : 'The field is empty' }}
        </output>
      </div>
      <epdf-stage class="stage">
        <ng-template epdfPage>
          <epdf-render-layer />
        </ng-template>
      </epdf-stage>
    </ng-container>

    <ng-template #loading><p class="loading">Loading…</p></ng-template>
  `,
})
export class App {
  private readonly form = inject(EpdfForm);
  private readonly stamp = inject(EpdfStamp);
  private readonly signature = inject(EpdfSignature);
  private readonly document = inject(EpdfDocument);
  private readonly stage = viewChild(EpdfStage);
  private done = false;
  protected readonly assetId = signal<string | null>(null);
  protected readonly drawn = signal(false);

  constructor() {
    this.signature.filled$.pipe(takeUntilDestroyed()).subscribe(() => this.drawn.set(true));
    this.signature.cleared$.pipe(takeUntilDestroyed()).subscribe(() => this.drawn.set(false));

    // On load: a signature field on the last page, a typed signature, drawn into the field.
    effect(() => {
      const page = this.document.pages().at(-1)?.ref;
      const stage = this.stage();
      if (this.form.status() !== 'ready' || !page || !stage || this.done) return;
      this.done = true;
      untracked(() => void this.setUp(page, stage));
    });
  }

  protected drawIn() {
    const assetId = this.assetId();
    if (assetId) void this.signature.fillField(APPROVAL, { assetId });
  }

  protected takeOut() {
    void this.signature.clearField(APPROVAL);
  }

  private async setUp(page: PageRef, stage: EpdfStage) {
    await this.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 this.stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
    const { asset } = await this.stamp.createAsset({
      libraryId: library.id,
      name: 'signature',
      label: 'Signature',
      mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
    });
    this.assetId.set(asset.id);
    await this.signature.fillField(APPROVAL, { assetId: asset.id });
  }
}

The key#

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

// 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:

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.ts

import { Component, inject } from '@angular/core';
import { EpdfSignature } from '@embedpdf/angular/signature';

@Component({
  selector: 'app-signature-list',
  template: `
    <ul>
      @for (sig of signature.signatures(); track sig.fieldName) {
        <li>{{ sig.fieldName }}: {{ sig.verdict?.summary ?? 'checking…' }}</li>
      }
    </ul>
  `,
})
export class SignatureList {
  protected readonly signature = inject(EpdfSignature);
}

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.ts

import { Component, inject } from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { EpdfSignature } from '@embedpdf/angular/signature';
import { toast } from './toast';

@Component({ selector: 'app-signature-guard', template: '' })
export class SignatureGuard {
  private readonly signature = inject(EpdfSignature);

  constructor() {
    this.signature.invalidationPredicted$.pipe(takeUntilDestroyed()).subscribe(({ field }) => {
      const name = this.signature.getSignature(field)?.fieldName;
      toast(`This change will break the signature in "${name}" when saved.`);
    });
  }
}

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.

Loading live preview…

import {
  ChangeDetectionStrategy,
  Component,
  computed,
  effect,
  inject,
  signal,
  untracked,
  viewChild,
  ViewEncapsulation,
} from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { EpdfDocument, EpdfDocumentGate, provideEmbedPdf } from '@embedpdf/angular/runtime';
import type { OpenInput, PageRef } from '@embedpdf/angular/runtime';
import { EpdfPageTemplate, EpdfStage, withStage } from '@embedpdf/angular/stage';
import { EpdfRenderLayer, withRender } from '@embedpdf/angular/render';
import { withInteraction } from '@embedpdf/angular/interaction';
import {
  EpdfAnnotation,
  EpdfAnnotationLayer,
  withAnnotation,
} from '@embedpdf/angular/annotation';
import { EpdfForm, toFieldRef, withForm } from '@embedpdf/angular/form';
import { EpdfStamp, withStamp } from '@embedpdf/angular/stamp';
import { createTestSigner, EpdfSignature, withSignature } from '@embedpdf/angular/signature';
import { localEngine } from '@embedpdf/engine';

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 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()) };
};

@Component({
  selector: 'demo-root',
  imports: [EpdfDocumentGate, EpdfStage, EpdfPageTemplate, EpdfRenderLayer, EpdfAnnotationLayer],
  providers: [
    provideEmbedPdf(
      { engine, initialDocuments: [{ source: ebook }] },
      withStage(),
      withRender(),
      withInteraction(),
      withAnnotation(),
      withForm(),
      withStamp({ assetEngine }),
      withSignature({
        key: () => signer,
        // Trust the demo key itself, so its signature checks out as 'valid'.
        trust: { anchors: async () => [(await signer).certificate] },
      }),
    ),
  ],
  changeDetection: ChangeDetectionStrategy.OnPush,
  styleUrl: './break-warning.css',
  encapsulation: ViewEncapsulation.None,
  template: `
    <ng-container *epdfDocumentGate="let document; fallback: loading">
      <div class="toolbar">
        <button type="button" class="button" [disabled]="!signed() || !page()" (click)="drawBox()">
          Draw a box on the page
        </button>
        <output class="readout">{{ status() }}</output>
        @if (warning(); as warning) {
          <output class="warning">{{ warning }}</output>
        }
      </div>
      <epdf-stage class="stage">
        <ng-template epdfPage>
          <epdf-render-layer />
          <epdf-annotation-layer />
        </ng-template>
      </epdf-stage>
    </ng-container>

    <ng-template #loading><p class="loading">Loading…</p></ng-template>
  `,
})
export class App {
  private readonly form = inject(EpdfForm);
  private readonly stamp = inject(EpdfStamp);
  private readonly annotation = inject(EpdfAnnotation);
  private readonly signature = inject(EpdfSignature);
  private readonly document = inject(EpdfDocument);
  private readonly stage = viewChild(EpdfStage);
  private done = false;

  /** The last page, which has room for the field. */
  protected readonly page = computed(() => this.document.pages().at(-1)?.ref);
  protected readonly signed = computed(() => this.signature.signatures()[0]);
  protected readonly status = computed(() => {
    const signed = this.signed();
    return signed
      ? `Signed by ${signed.signer.name}: ${signed.verdict?.summary ?? 'checking…'}`
      : 'Signing…';
  });
  protected readonly warning = signal<string | null>(null);

  constructor() {
    // The moment a change would break a signature once it's saved, as Acrobat warns.
    this.signature.invalidationPredicted$.pipe(takeUntilDestroyed()).subscribe(({ field }) => {
      const name = this.signature.getSignature(field)?.fieldName;
      this.warning.set(`This change will break the signature in "${name}" when saved.`);
    });

    // On load: a signature field on the last page, signed by Ada with a typed signature.
    effect(() => {
      const page = this.page();
      const stage = this.stage();
      if (this.form.status() !== 'ready' || !page || !stage || this.done) return;
      this.done = true;
      untracked(() => void this.signDocument(page, stage));
    });
  }

  protected drawBox() {
    const page = this.page();
    if (!page) return;
    void this.annotation.create(page, {
      subtype: 'square',
      box: { x: 320, y: 560, width: 140, height: 64 },
      color: '#e11d48',
      strokeWidth: 2,
    });
  }

  private async signDocument(page: PageRef, stage: EpdfStage) {
    await this.form.create({
      family: 'signature',
      name: 'approval',
      widgets: [{ page, rect: { x: 72, y: 560, width: 220, height: 64 } }],
    });
    stage.goToPage(page);
    const { library } = await this.stamp.createLibrary('Ada Lovelace', { kind: 'signatures' });
    const { asset } = await this.stamp.createAsset({
      libraryId: library.id,
      name: 'signature',
      label: 'Signature',
      mark: { kind: 'text', text: 'Ada Lovelace', fontFamily: 'times-italic', color: '#1d2b53' },
    });
    await this.signature.sign({ field: toFieldRef('approval'), mark: { assetId: asset.id } });
  }
}

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:

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' },
});

signature.signerRows() 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, 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:

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

Event	Fires when	Show
`targetChanged$`	A field became the target	your signatures panel
`signRequested$`	In `'ask'` mode, a mark was dropped on a field	your sign dialog
`inspectionRequested$`	A signed field was clicked	the signature’s details

Methods#

Everything inject(EpdfSignature) 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
`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
`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
`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
`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
`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
`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
`setTarget(field)`	Makes a field the target, where the next mark the person picks goes; `null` clears. “Sign here” in a form
`requestInspection(field)`	Asks your UI to show a signed field’s details, as clicking it does: `inspectionRequested$` fires
`getMode()`	The mode in effect: the `mode` setting, or its default. 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
`getSettings()`, `updateSettings(changes)`, `resetSettings()`	Reads the settings, changes them while the app runs, or goes back to what you registered. In a component, use `inject(EpdfSignature).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#

Every value is a signal on inject(EpdfSignature): read it in a template or a computed(), and your view updates when it 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 inject(EpdfSignature).settings() 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.ts

import { Component, inject } from '@angular/core';
import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
import { EpdfSignature } from '@embedpdf/angular/signature';
import { showWarning } from './warnings';

@Component({ selector: 'app-save-warning', template: '' })
export class SaveWarning {
  constructor() {
    inject(EpdfSignature)
      .invalidationPredicted$.pipe(takeUntilDestroyed())
      .subscribe(() => showWarning('Saving this change will break a signature.'));
  }
}

Event	Fires when	Carries
`signed$`	A field was signed, whoever signed it	`field`, `result`, `origin`
`filled$`, `cleared$`	A mark was drawn into a field, or removed	`field`
`validated$`	The signatures were checked	`verdicts`
`protectionChanged$`	What the signatures allow changed	`protection`
`invalidationPredicted$`	A change would break a signature once saved	`field`, `detail`
`targetChanged$`	A field became the target, or the target was cleared	`field` (`null` when cleared)
`signRequested$`	In `'ask'` mode, a mark was dropped on a field	`field`, `mark`
`inspectionRequested$`	A signed field was clicked	`field`
`settingsChanged$`	The settings changed	`settings`, `changed`

result is what sign() resolves. “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. 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.

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