Convert the base-64 encoded blob generated on the server into an array buffer for encryption.

convertPDFData.js

   /*     
    * Handles client-side conversion of document 
    * data from server to a format we can use for encryption.
    * Called in both download & email workflows.  
    *
    * @return {arrayBuffer} Array Buffer of the document content.
    */    
         async function convertPDFData() {
           // Gets document content; converts
           // document content back into a usable
           // PDF-type blob.
           var blobB64 = await genPDF();
           var binary = atob(blobB64.replace(/\s/g, ''));
           var len = binary.length;
           var buffer = new ArrayBuffer(len);
           var view = new Uint8Array(buffer);
           for (var i =0; i < len; i++) {
               view[i] = binary.charCodeAt(i);
           }
           var blob = new Blob([view], {type: "application/pdf"});
           // Generates an array buffer from the blob.
           // Will be used as source data for encryption.
           var arrayBuffer = null;
           arrayBuffer = await new Response(blob).arrayBuffer();
           return arrayBuffer;
         }