The pdf annotation software I started using early on my career was Mendeley, back when it was an open-source independent project. Then it was bought my Elsevier, its code became private, and a sort of social network was built around its user data-base. No thank you, I won't give my data to such an evil publishing machine.
I then switched to Polar. It was independent, light-weight, open-source... Really nice! But the creators of the project started complaining they were not receiving any support from users (before they even released their first stable version), they started using google code, closed the source-code, and then again everything went to downhill...
I thought I would never find a decent, open-source, independently developed academic library. I annotate my pdfs, write comments on them, etc. And I need to have the ordered by topic, authors, and all the relevant metadata.
And then I realized the answer was in front of me this whole time! Okular! The pdf reader that comes with KDE (linux) implemented a lot of options that allow to highlight, underline, annotate, etc your pdfs. The interface is great, the software is very lightweight, works flawlessly, and I can be sure it will remain open-source.
The only thing I am missing is a dedicated library to manage my pdfs, but honestly, I can do that myself by keeping an ordered and systematic system to store my library on my hard-drives, with some backup in the cloud.

#linux #foss #pdfs #Mendeley #Polar #Okular #Kde #opensource #academia #science