It would be very useful to be able to share the document (via Google Drive's sharing capabilities) when the document is opened in this add-on.
The reading experience is pleasant, but opening a document and then sharing is a bit of a hassle.
A typical user flow in Google Drive is to start searching for a document and usually, you will see the document in the suggested items that are shown before you hit enter to submit your full search query. The PDF opens in your add-on which is nice. However, if you as a user come to the conclusion that you want to share the document, you can't do that from the opened view in the add-on. You would need to go back to Google Drive, do the search again (if you remember what you searched for), hit enter to get the search result on the page in Google Drive, and then right click on the file to open the Sharing dialog.

I hope this helps in improving your add-on.

Kind regards,

Jasper