If the reports are somewhat technical (written with Latex for example), check out sioyek: https://sioyek.info/. It's a PDF reader mainly for academic use.

Sioyek has made reading and reviewing papers SO much easier and it's really, really convenient... once you get the hang of it. It takes a bit of time to get used to all the things, but it's worth it. I also review students' theses with it. Highlighting colors and adding comments is super easy (select text, h+g (green highlight), type comment).

If you have want to export your notes and comments, you will need this script though: https://github.com/ahrm/sioyek/blob/main/scripts/embedded_annotations.py