fix: normalize and flatten annotations

packages/lib/server-only/document/seal-document.ts

@@ -2,7 +2,7 @@
 
 import { nanoid } from 'nanoid';
 import path from 'node:path';
-import { PDFDocument, PDFSignature, rectangle } from 'pdf-lib';
+import { PDFDocument } from 'pdf-lib';
 
 import PostHogServerClient from '@documenso/lib/server-only/feature-flags/get-post-hog-server-client';
 import { DOCUMENT_AUDIT_LOG_TYPE } from '@documenso/lib/types/document-audit-logs';
@@ -15,7 +15,9 @@ import { signPdf } from '@documenso/signing';
 import type { RequestMetadata } from '../../universal/extract-request-metadata';
 import { getFile } from '../../universal/upload/get-file';
 import { putFile } from '../../universal/upload/put-file';
+import { flattenAnnotations } from '../pdf/flatten-annotations';
 import { insertFieldInPDF } from '../pdf/insert-field-in-pdf';
+import { normalizeSignatureAppearances } from '../pdf/normalize-signature-appearances';
 import { triggerWebhook } from '../webhooks/trigger/trigger-webhook';
 import { sendCompletedEmail } from './send-completed-email';
 
@@ -91,31 +93,10 @@ export const sealDocument = async ({
 
   const doc = await PDFDocument.load(pdfData);
 
-  const form = doc.getForm();
+  // Normalize and flatten layers that could cause issues with the signature
-
+  normalizeSignatureAppearances(doc);
-  // Remove old signatures
+  flattenAnnotations(doc);
-  for (const field of form.getFields()) {
+  doc.getForm().flatten();
-    if (field instanceof PDFSignature) {
-      field.acroField.getWidgets().forEach((widget) => {
-        widget.ensureAP();
-
-        try {
-          widget.getNormalAppearance();
-        } catch (e) {
-          const { context } = widget.dict;
-
-          const xobj = context.formXObject([rectangle(0, 0, 0, 0)]);
-
-          const streamRef = context.register(xobj);
-
-          widget.setNormalAppearance(streamRef);
-        }
-      });
-    }
-  }
-
-  // Flatten the form to stop annotation layers from appearing above documenso fields
-  form.flatten();
 
   for (const field of fields) {
     await insertFieldInPDF(doc, field);

packages/lib/server-only/pdf/flatten-annotations.ts

@@ -0,0 +1,63 @@
+import { PDFAnnotation, PDFRef } from 'pdf-lib';
+import {
+  PDFDict,
+  type PDFDocument,
+  PDFName,
+  drawObject,
+  popGraphicsState,
+  pushGraphicsState,
+  rotateInPlace,
+  translate,
+} from 'pdf-lib';
+
+export const flattenAnnotations = (document: PDFDocument) => {
+  const pages = document.getPages();
+
+  for (const page of pages) {
+    const annotations = page.node.Annots()?.asArray() ?? [];
+
+    annotations.forEach((annotation) => {
+      if (!(annotation instanceof PDFRef)) {
+        return;
+      }
+
+      const actualAnnotation = page.node.context.lookup(annotation);
+
+      if (!(actualAnnotation instanceof PDFDict)) {
+        return;
+      }
+
+      const pdfAnnot = PDFAnnotation.fromDict(actualAnnotation);
+
+      const appearance = pdfAnnot.ensureAP();
+
+      // Skip annotations without a normal appearance
+      if (!appearance.has(PDFName.of('N'))) {
+        return;
+      }
+
+      const normalAppearance = pdfAnnot.getNormalAppearance();
+      const rectangle = pdfAnnot.getRectangle();
+
+      if (!(normalAppearance instanceof PDFRef)) {
+        // Not sure how to get the reference to the normal appearance yet
+        // so we should skip this annotation for now
+        return;
+      }
+
+      const xobj = page.node.newXObject('FlatAnnot', normalAppearance);
+
+      const operators = [
+        pushGraphicsState(),
+        translate(rectangle.x, rectangle.y),
+        ...rotateInPlace({ ...rectangle, rotation: 0 }),
+        drawObject(xobj),
+        popGraphicsState(),
+      ].filter((op) => !!op);
+
+      page.pushOperators(...operators);
+
+      page.node.removeAnnot(annotation);
+    });
+  }
+};

packages/lib/server-only/pdf/normalize-signature-appearances.ts

@@ -0,0 +1,26 @@
+import type { PDFDocument } from 'pdf-lib';
+import { PDFSignature, rectangle } from 'pdf-lib';
+
+export const normalizeSignatureAppearances = (document: PDFDocument) => {
+  const form = document.getForm();
+
+  for (const field of form.getFields()) {
+    if (field instanceof PDFSignature) {
+      field.acroField.getWidgets().forEach((widget) => {
+        widget.ensureAP();
+
+        try {
+          widget.getNormalAppearance();
+        } catch {
+          const { context } = widget.dict;
+
+          const xobj = context.formXObject([rectangle(0, 0, 0, 0)]);
+
+          const streamRef = context.register(xobj);
+
+          widget.setNormalAppearance(streamRef);
+        }
+      });
+    }
+  }
+};

packages/signing/helpers/add-signing-placeholder.ts

@@ -1,5 +1,6 @@
 import {
   PDFArray,
+  PDFDict,
   PDFDocument,
   PDFHexString,
   PDFName,
@@ -16,7 +17,7 @@ export type AddSigningPlaceholderOptions = {
 
 export const addSigningPlaceholder = async ({ pdf }: AddSigningPlaceholderOptions) => {
   const doc = await PDFDocument.load(pdf);
-  const pages = doc.getPages();
+  const [firstPage] = doc.getPages();
 
   const byteRange = PDFArray.withContext(doc.context);
 
@@ -25,7 +26,8 @@ export const addSigningPlaceholder = async ({ pdf }: AddSigningPlaceholderOption
   byteRange.push(PDFName.of(BYTE_RANGE_PLACEHOLDER));
   byteRange.push(PDFName.of(BYTE_RANGE_PLACEHOLDER));
 
-  const signature = doc.context.obj({
+  const signature = doc.context.register(
+    doc.context.obj({
       Type: 'Sig',
       Filter: 'Adobe.PPKLite',
       SubFilter: 'adbe.pkcs7.detached',
@@ -33,56 +35,62 @@ export const addSigningPlaceholder = async ({ pdf }: AddSigningPlaceholderOption
       Contents: PDFHexString.fromText(' '.repeat(8192)),
       Reason: PDFString.of('Signed by Documenso'),
       M: PDFString.fromDate(new Date()),
-  });
+    }),
+  );
 
-  const signatureRef = doc.context.register(signature);
+  const widget = doc.context.register(
-
+    doc.context.obj({
-  const widget = doc.context.obj({
       Type: 'Annot',
       Subtype: 'Widget',
       FT: 'Sig',
       Rect: [0, 0, 0, 0],
-    V: signatureRef,
+      V: signature,
       T: PDFString.of('Signature1'),
       F: 4,
-    P: pages[0].ref,
+      P: firstPage.ref,
-  });
+      AP: doc.context.obj({
-
+        N: doc.context.register(doc.context.formXObject([rectangle(0, 0, 0, 0)])),
-  const xobj = widget.context.formXObject([rectangle(0, 0, 0, 0)]);
+      }),
-
-  const streamRef = widget.context.register(xobj);
-
-  widget.set(PDFName.of('AP'), widget.context.obj({ N: streamRef }));
-
-  const widgetRef = doc.context.register(widget);
-
-  let widgets = pages[0].node.get(PDFName.of('Annots'));
-
-  if (widgets instanceof PDFArray) {
-    widgets.push(widgetRef);
-  } else {
-    const newWidgets = PDFArray.withContext(doc.context);
-
-    newWidgets.push(widgetRef);
-
-    pages[0].node.set(PDFName.of('Annots'), newWidgets);
-
-    widgets = pages[0].node.get(PDFName.of('Annots'));
-  }
-
-  if (!widgets) {
-    throw new Error('No widgets');
-  }
-
-  pages[0].node.set(PDFName.of('Annots'), widgets);
-
-  doc.catalog.set(
-    PDFName.of('AcroForm'),
-    doc.context.obj({
-      SigFlags: 3,
-      Fields: [widgetRef],
     }),
   );
 
+  let widgets: PDFArray;
+
+  try {
+    widgets = firstPage.node.lookup(PDFName.of('Annots'), PDFArray);
+  } catch {
+    widgets = PDFArray.withContext(doc.context);
+
+    firstPage.node.set(PDFName.of('Annots'), widgets);
+  }
+
+  widgets.push(widget);
+
+  let arcoForm: PDFDict;
+
+  try {
+    arcoForm = doc.catalog.lookup(PDFName.of('AcroForm'), PDFDict);
+  } catch {
+    arcoForm = doc.context.obj({
+      Fields: PDFArray.withContext(doc.context),
+    });
+
+    doc.catalog.set(PDFName.of('AcroForm'), arcoForm);
+  }
+
+  let fields: PDFArray;
+
+  try {
+    fields = arcoForm.lookup(PDFName.of('Fields'), PDFArray);
+  } catch {
+    fields = PDFArray.withContext(doc.context);
+
+    arcoForm.set(PDFName.of('Fields'), fields);
+  }
+
+  fields.push(widget);
+
+  arcoForm.set(PDFName.of('SigFlags'), PDFNumber.of(3));
+
   return Buffer.from(await doc.save({ useObjectStreams: false }));
 };