The ability to link externally (ie to a URL, or to a pdf in my files) or internally (ie within GoodNotes) would make GN a lot more viable as a working tool.

I've just started a degree so have years of study ahead of me. Finding the right tool at the outset is vital, so that my notes will be consistent in terms of file type, cross-file compatibility etc. - with study notes I NEED to be able to link to research sources / related GN notes etc.

This is a reasonable expectation in 2021. The lack of this functionality (as well as other points re editing pen tool I've made separate suggestions for) has me questioning whether I continue using the app at all; GN currently does not strike me a serious tool. It looks nice but it's a box of crayons when I need something with a more grown up engine.