fix: handle signature annotations

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

@@ -2,7 +2,7 @@
 
 import { nanoid } from 'nanoid';
 import path from 'node:path';
-import { PDFDocument } from 'pdf-lib';
+import { PDFDocument, PDFSignature, rectangle } 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';
@@ -91,8 +91,31 @@ export const sealDocument = async ({
 
   const doc = await PDFDocument.load(pdfData);
 
+  const form = doc.getForm();
+
+  // Remove old signatures
+  for (const field of form.getFields()) {
+    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
-  doc.getForm().flatten();
+  form.flatten();
 
   for (const field of fields) {
     await insertFieldInPDF(doc, field);

packages/signing/helpers/addSigningPlaceholder.ts

@@ -1,5 +1,13 @@
 import signer from 'node-signpdf';
-import { PDFArray, PDFDocument, PDFHexString, PDFName, PDFNumber, PDFString } from 'pdf-lib';
+import {
+  PDFArray,
+  PDFDocument,
+  PDFHexString,
+  PDFName,
+  PDFNumber,
+  PDFString,
+  rectangle,
+} from 'pdf-lib';
 
 export type AddSigningPlaceholderOptions = {
   pdf: Buffer;
@@ -39,6 +47,12 @@ export const addSigningPlaceholder = async ({ pdf }: AddSigningPlaceholderOption
     P: pages[0].ref,
   });
 
+  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'));