Combining Multiple Invoices into a Single PDF Document

I am trying to combine multiple invoices into a single pdf which would then be emailed to the customer.
I looked up the forums and found some help. https://usergroup.netsuite.com/users/forum/platform-areas/customization/suitescript-custom-code/355188-combine-multiple-invoices-into-1-pdf-file
Based on that this is what I have been trying so far.. The file that gets send is unreadable and most likely the encoding is all incorrect?
Below is the code


var statementFile1 = nlapiPrintRecord('TRANSACTION', '5778', 'PDF');
  //statementFile1.setEncoding('UTF-8'); // doesnt help..
var statementFile2 = nlapiPrintRecord('TRANSACTION', '5782', 'PDF');
var statementFile3 = nlapiPrintRecord('TRANSACTION', '5766', 'PDF');

var xml = "<?xml version="1.0"?>\n<!DOCTYPE pdf PUBLIC "-//big.faceless.org//report" "report-1.1.dtd">\n";