Okular has a functionality allowing to insert LaTeX code inside inline notes by simply putting it between `$$`, like this: $$\sqrt 2$$.
Okular suggests texlive-binaries as dependencies. The how to do it is described here: https://docs.kde.org/trunk5/en/kdegraphics/okular/annotations.html Basically you write your inline note, then you double click it in order to edit it, and there, there is a messages saying to click it in order to render the Latex code. But then, what happens for me, even though I've installed the "suggested" texlive-binaries, and rebooted in between, is that I get a message saying "cannot find latex executable". I've probably missed something. The functionality is suppose to be here since 2012. It is the first time I try it. Just discovered it as a matter of fact. Chris