Check out
https://github.com/jsbain/ios-url-scheme-extractor
then run python ios-url-scheme-extractor.py
Select the app, and it should populate with the url scheme.
Basically, many, if not all, apps have a url scheme, even if not published.
I suspect GoodNotes has one (or had one, as of version 4.4)... it is a sort of random set of characters:
db-f4jb04w77pqlxjc
I suspect that app has DropBox integration, hence the db prefix. This could be version dependent.
The trick will be figuring out a way to launch the app WITH an attachment.... which might be impossible without using something like ctypes. You could first upload to dropbox, then launch GoodNotes, and use its dropbox integration to download it from dropbox... not ideal but an option