PDF annotation on Android

Hi there, I often need to read PDFs and annotate things in them (highlight, add comments, mark and sign them even) on my Android. For now I’m using Adobe Reader. Luckily I’m on Graphene and just disabled network for Adobe Reader. From what I understand it can still share info with other apps though and if they have network access, they can send info out.

So, my questions, is this info sharing really a concern (i dont have play services installed)? And, do you have FOSS alternatives? That would be even better of course, but i couldn’t find anything.

Cheers and let me know if this isn’t really the forum to ask that