Maybe this code can help you .
function toPdf(id){
SpreadsheetApp.flush();
// var ssDoc = DriveApp.getFileById(SpreadsheetApp.getActiveSpreadsheet().getId());
var ssDoc = DriveApp.getFileById(id);
var pdf = DriveApp.createFile(ssDoc.getAs(MimeType.PDF));
return pdf.getBlob().getBytes();
}