fix: normalize pdf on the server

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

@@ -0,0 +1,18 @@
+import { PDFDocument } from 'pdf-lib';
+
+import { flattenAnnotations } from './flatten-annotations';
+import { flattenForm, removeOptionalContentGroups } from './flatten-form';
+
+export const normalizePdf = async (pdf: Buffer) => {
+  const pdfDoc = await PDFDocument.load(pdf).catch(() => null);
+
+  if (!pdfDoc) {
+    return pdf;
+  }
+
+  removeOptionalContentGroups(pdfDoc);
+  flattenForm(pdfDoc);
+  flattenAnnotations(pdfDoc);
+
+  return Buffer.from(await pdfDoc.save());
+};