Convert PDF to Doc with Google Script Editor

I'm looking to convert PDF to google Doc in Drive using Google Script Editor. However keep getting error message "Converting from application/pdf to application/doc is not supported". Is this conversion possible in script? My attempt as below, would be great to hear any advice.

function convertdPDF2doc() {
  var pdffile = DriveApp.getFileById();
  var pdfblob = pdffile.getAs('application/doc');

  pdfblob.setName(doc.getName() + ".doc");
  DriveApp.createFile(docblob);

}