Add error handling on pdf parsing

javascript/src/utilities/pdfUtilities.js

@@ -612,10 +612,15 @@ async function appendSig(pdf, root, rootSuccessor, date, signingCert, certificat
 }
 
 function loadPdf(pdfArray) {
-    var pdf = new pdfjsCoreDocument.PDFDocument(false, pdfArray, '');
-    pdf.parseStartXRef();
-    pdf.parse();
-    return pdf;
+    try {
+        var pdf = new pdfjsCoreDocument.PDFDocument(false, pdfArray, '');
+        pdf.parseStartXRef();
+        pdf.parse();
+        return pdf;
+    }
+    catch(err) {
+      throw new Error('Error parsing PDF: ' + err);
+    }
 }