chore: sign document

packages/signing/helpers/addSigningPlaceholder.ts

@@ -0,0 +1,73 @@
+import signer from 'node-signpdf';
+import { PDFArray, PDFDocument, PDFHexString, PDFName, PDFNumber, PDFString } from 'pdf-lib';
+
+export type AddSigningPlaceholderOptions = {
+  pdf: Buffer;
+};
+
+export const addSigningPlaceholder = async ({ pdf }: AddSigningPlaceholderOptions) => {
+  const doc = await PDFDocument.load(pdf);
+  const pages = doc.getPages();
+
+  const byteRange = PDFArray.withContext(doc.context);
+
+  byteRange.push(PDFNumber.of(0));
+  byteRange.push(PDFName.of(signer.byteRangePlaceholder));
+  byteRange.push(PDFName.of(signer.byteRangePlaceholder));
+  byteRange.push(PDFName.of(signer.byteRangePlaceholder));
+
+  const signature = doc.context.obj({
+    Type: 'Sig',
+    Filter: 'Adobe.PPKLite',
+    SubFilter: 'adbe.pkcs7.detached',
+    ByteRange: byteRange,
+    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.obj({
+    Type: 'Annot',
+    Subtype: 'Widget',
+    FT: 'Sig',
+    Rect: [0, 0, 0, 0],
+    V: signatureRef,
+    T: PDFString.of('Signature1'),
+    F: 4,
+    P: pages[0].ref,
+  });
+
+  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],
+    }),
+  );
+
+  return Buffer.from(await doc.save({ useObjectStreams: false }));
+};