How to use a google apps script in multiple documents

Question

I have a google apps script that I want to use in multiple documents. I also may want to change it later in those documents, so it is imperative that I use the same

Answer 1

Sorry, my reputation was too low to add a comment. :( In Giuseppe's answer use this for find docs - minor change

function findDoc(pros) {
  var ui =  DocumentApp.getUi();
  var pro = ui.prompt(pros, 'URL:', ui.ButtonSet.OK);
  var url = pro.getResponseText();
  return DocumentApp.openByUrl(url);
}