Server-side Google Apps Script code to generate base 64-encoded PDF blob from Google Doc.

createPDF.gs

function createPDF() {
  var docBlob = DocumentApp.getActiveDocument().getBlob();
  docBlob.setName(doc.getName() + '.pdf');
  var blobB64 = Utilities.base64Encode(docBlob.getBytes());
  return blobB64;
}