I use Master PDF Editor for that it not only functions as a PDF reader but also is a full fledged PDF editor. Of course it's a paid closed-source software and since it's also a full fledged PDF editor it's indeed a total overkill if you want to just highlight PDFs. But in my experience it the best software available for Linux to interact with PDFs. Of course there's yet another alternative called Qoppa PDF Studio Pro which has same features but I prefer Master PDF Editor because it is a native Linux app while Qoppa PDF Studio Pro is written in JAVA and requires JAVA runtime to work. And truth be told right now you may not need a PDF reader with full fledged PDF editing capabilities but you may need one in future so why settle for a mere PDF reader go directly for something which offers you both PDF reading and editing capabilities.