Runs server-side function to return the contents of the document in base64 format.

pdfToClient.js

   /*      
    * Runs server-side function to return the contents
    * of the document in base64 format.
    *
    * @return {string} Base 64'd document content.
    */    
         function genPDF() {
           return new Promise(function(resolve, reject) {
             google.script.run
               .withSuccessHandler(function(blobB64) {
                 resolve(blobB64);
               })
               .createPDF();
           });
         }