The Google Script will create a new event in the specified Google Calendar and will attach a file from Google Drive into the event.

Google Calendar API only allows file attachments from Google Drive and you can include a maximum of 25 attachment per event. The attachments can be specified either by File ID or by File URL. The Advanced Calendar API should be enabled from your Google Console.

// Credits / References
// https://developers.google.com/google-apps/calendar/v3/reference/events
// http://stackoverflow.com/questions/34853043

function createEvent() {
  var calendarId = '{{Google Calendar Id}}';

  // April 20, 2016 10:00:00 AM
  var start = new Date(2016, 3, 20, 10, 0, 0);

  // April 20, 2016 10:30:00 AM
  var end = new Date(2016, 3, 20, 10, 30, 0);

  var fileName = 'Appraisal Guidlines.pdf';

  // Get the Drive ID of the file attachments
  // Only Google Drive file are support in Google Calendar
  var fileId = DriveApp.getFilesByName(fileName).next().getId();

  var calendarEvent = {
    summary: 'Performance Appraisal',
    description: 'Submit Appraisal Document for March.',
    location: '10 Hanover Square, NY 10005',
    start: {
      dateTime: start.toISOString(),
    },
    end: {
      dateTime: end.toISOString(),
    },
    attachments: [
      {
        fileId: fileId,
        title: fileName,
      },
    ],
    attendees: [
      {
        email: 'employee1@ctrlq.org',
      },
      {
        email: 'employee2@labnol.org',
      },
    ],
  };

  // Set supportsAttachments to true
  // if the calendarEvent object has one or more file attachments
  calendarEvent = Calendar.Events.insert(calendarEvent, calendarId, {
    supportsAttachments: true,
  });

  Logger.log('Event with attachment created. Event ID is %s' + calendarEvent.getId());

  // For debugging the output
  Logger.log(calendarEvent);
}