do not overwrite the AcroForm when it was already there

refs #198
vbuch · Nov 14, 2023 · 4899dcf · 4899dcf
1 parent ac61226
commit 4899dcf
Showing 1 changed file with 24 additions and 8 deletions.
diff --git a/packages/placeholder-pdf-lib/src/pdflibAddPlaceholder.js b/packages/placeholder-pdf-lib/src/pdflibAddPlaceholder.js
@@ -6,7 +6,7 @@ import {
     SUBFILTER_ADOBE_PKCS7_DETACHED,
 } from '@signpdf/utils';
 import {
-    PDFArray, PDFHexString, PDFName, PDFNumber, PDFString, toHexStringOfMinLength,
+    PDFArray, PDFDict, PDFHexString, PDFName, PDFNumber, PDFString, toHexStringOfMinLength,
 } from 'pdf-lib';
 
 /**
@@ -95,12 +95,28 @@ export const pdflibAddPlaceholder = ({
         pdfDoc.context.obj([widgetDictRef]),
     );
 
-    // Reference the widget in the a new AcroForm
-    pdfDoc.catalog.set(
-        PDFName.of('AcroForm'),
-        pdfDoc.context.obj({
-            SigFlags: SIG_FLAGS.SIGNATURES_EXIST | SIG_FLAGS.APPEND_ONLY,
-            Fields: [widgetDictRef],
-        }),
+    // Add an AcroForm or update the existing one
+    let acroForm = pdfDoc.catalog.lookupMaybe(PDFName.of('AcroForm'), PDFDict);
+    if (typeof acroForm === 'undefined') {
+        // Need to create a new AcroForm
+        acroForm = pdfDoc.context.obj({Fields: []});
+    }
+
+    /**
+     * @type {PDFNumber}
+     */
+    let sigFlags;
+    if (acroForm.has(PDFName.of('SigFlags'))) {
+        // Already has some flags, will merge
+        sigFlags = acroForm.get(PDFName.of('SigFlags'));
+    } else {
+        // Create blank flags
+        sigFlags = PDFNumber.of(0);
+    }
+    const updatedFlags = PDFNumber.of(
+        sigFlags.asNumber() | SIG_FLAGS.SIGNATURES_EXIST | SIG_FLAGS.APPEND_ONLY,
     );
+    acroForm.set(PDFName.of('SigFlags'), updatedFlags);
+    const fields = acroForm.get(PDFName.of('Fields'));
+    fields.push(widgetDictRef);
 };