Workflow to annotate PDFs stored in a Cryptomator vault in OneDrive (on iOS)?

I work with PDFs quite a bit and like to annotate them on my iPad. With OneDrive, this process is simple - I can edit my PDFs directly in the OneDrive app with the apps basic annotation tool (which is what I do now), or I can edit my PDFs with one of the third party annotation apps available (all of which only support integration with the big, mainstream cloud providers) - this I haven’t tried yet, mostly because the annotation tools within the OneDrive app have been good enough for me.

Obviously, this functionality has been broken ever since I’ve transitioned to saving all of my files to a Cryptomator vault located inside of OneDrive. I can still see the files through the Cryptomator app, but can no longer edit them in OneDrive. I haven’t even figured out how to save PDFs from my iPad to the vault in OneDrive; which is a problem for me, as I usually add new PDFs to OneDrive from both of my devices (iPad and PC). I haven’t tried any of the popular PDF annotation apps on iOS yet because many of them are paid and I’m not sure if integration with Cryptomator is even possible (considering that many of these apps don’t even support integration with cloud providers outside of OneDrive, Box, Google Drive, and Dropbox).

For those of you who annotate PDFs cross-platform and also use Cryptomator - what workflow has been best for you?