I have made an add-ons for Google app scripts . Now I want to add it in every document in one folder. How can i do that?
In this tutorial https://developers.google.com/apps-script/quickstart/docs, it only uses for one document.
If your add-on was published to Google Marketplace/Chrome Web Store and you installed it from there, and you are the owner of all the docs in the folder, that add-on should be available in your docs under Add-ons menu. I think it's the same for domain-specific add-ons as well (have no way to check it at the moment).
If you just created an add-on in a doc-bound script, then the add-on will only be available in that doc. To add it to other docs, you will have to copy your script into those docs manually - there is no API way to do it.