Can "Page Sizer" Google Docs add-on read my Google Docs?

https://workspace.google.com/marketplace/app/page_sizer/595382898724

The "Page Sizer" add-on to Google Docs would be wonderful!

But even though I read through their:

https://apps.burnskids.com/terms.htmland:https://apps.burnskids.com/privacy.html

I still don't have information about that that after adding this addon to my Google Docs, will they be able to read all my Google Docs as a third party?

Or they just add some CSS to Google Docs and they cannot see what am I writing in my "private" Google Docs files.