FOSS: Best PDF Reader and Annotator

PDF Exchange Viewer is a Free Open Source Software (FOSS) that allows users to not only read PDF (like Adobe) but allows you to highlight, put sticky notes, and even write/draw on your files.

For someone like me, who can't read without writing all over my text, this is the solution and that finally allowed me to stop printing my journal articles and start reading and annotating them digitally.