fix error when no signatures

dist/lib/index.js

@@ -6,7 +6,13 @@ const signatureUtils_1 = require("./signatureUtils");
 const verify_1 = require("./verify");
 const verifyPDF = (pdf) => {
     const pdfBuffer = (0, generalUtils_1.preparePDF)(pdf);
-    (0, generalUtils_1.checkForSubFilter)(pdfBuffer);
+    try {
+        (0, generalUtils_1.checkForSubFilter)(pdfBuffer);
+    }
+    catch (error) {
+        console.log("no supported signatures found");
+        return null;
+    }
     try {
         const { signatureStr, signedData, signatureMeta } = (0, signatureUtils_1.extractSignature)(pdfBuffer);
         const signatures = signedData.map((_signed, index) => {

src/lib/index.ts

@@ -4,7 +4,13 @@ import { verify } from "./verify";
 
 export const verifyPDF = (pdf: Buffer) => {
   const pdfBuffer = preparePDF(pdf);
-  checkForSubFilter(pdfBuffer);
+  try {
+    checkForSubFilter(pdfBuffer);
+  } catch (error) {
+    console.log("no supported signatures found");
+    return null;
+  }
+
   try {
     const { signatureStr, signedData, signatureMeta } =
       extractSignature(pdfBuffer);