Looking for a way to create a custom menu on Google Apps Script available across ALL my Google Docs, not just the one for which I created the script. The function itself works properly, it is the setup/trigger rather that is giving me trouble. Not sure if this is possible, given I'm seeing info saying Custom Menus must be bound to a particular document (rather than the whole object), so open to other suggestions too - the goal is to be able to apply a specific template to a Google Doc when I'd like (they will always be created in the same folder).

function OnOpen(e) {
  DocumentApp.getUi().createMenu('Template Options')
      .addItem('Apply Customer Note Template', 'menuItem1')
      .addToUi()
}

function menuItem1() {
  var body = DocumentApp.getActiveDocument().getBody();


  var OppTitle = body.appendParagraph("Opportunity Name");
  OppTitle.setHeading(DocumentApp.ParagraphHeading.TITLE);
  OppTitle.setAlignment(DocumentApp.HorizontalAlignment.CENTER);

...

  DocumentApp.getUi().alert('Customer Template applied.');
  
  }