Okular is a fantastic KDE app that lets you view and annotate various document formats, including PDFs.
Did we mention it is fantastic? Well, you can help us make it even better!
Join us tomorrow, November 17, for an all-day bug-hunting session in #kde-bugs IRC channel on freenode.
More details about the Okular Bug Day here:
https://andrewcrouthamel.wordpress.com/2018/11/14/kde-bugsquad-okular-bug-day-on-november-17th-2018/