function getDocs() {
  var folderId= '<<PUT YOUR FOLDER ID HERE>>';

  var pdfFolder = DriveApp.getFolderById(folderId).createFolder('PDFs');
  var files = DriveApp.getFolderById(folderId).getFilesByType(MimeType.GOOGLE_DOCS);

  while(files.hasNext()) {
    var file = files.next();

    var pdf = file.getAs('application/pdf');

    pdfFolder.createFile(pdf.copyBlob());
  }
}