The Google Documents API doesn’t offer a method to get the number of pages in a document. Dave Lam has an interesting workaround that will not only help you count the pages in a Google Document but of any PDF file that’s in your Google Drive.

The idea is to convert the Google Document into PDF and then parse the content of the PDF document as a text file using Regular Expressions.

function countPDFPages() {

  var blob = DocumentApp.getActiveDocument().getAs("application/pdf");
  var data = blob.getDataAsString();

  var re = /Pages\\/Count (\\d+)/g;
  var match;
  var pages = 0;

  while (match = re.exec(data)) {

    var value = parseInt(match[1]);

    if (value > pages) {
      pages = value;
    }

  }

  Logger.log("Total PDF pages = " + pages);

  return pages;
}