Question about the Google Docs add-on: do you have access to all documents on Google docs, at any time?
Add-on has access only to files in which the add-on is used. More information can be found here https://developers.google.com/apps-script/guides/services/au...
In addition your document is shared with an editor, but only after you agree to work with him.
Question about the Google Docs add-on: do you have access to all documents on Google docs, at any time?