Set the pdf size when emailing it as an attachment

Question

How do I set the pdf size as A4? Is it possible to force the sheet into a single pdf page?

function sendSheet() {
  var message = {
    to: "EMAIL",
    subject: "SUBJECT",
    body: "BODY",
    attachments: [SpreadsheetApp.openByUrl("URL").getAs(MimeType.PDF).setName("NAME.pdf")]
  }
  MailApp.sendEmail(message);