Annotations support latex by inserting $$ CODE $$, but this feature seems to be not documented in the Okular manual.
Git commit fbd0fd69af1e4f6d10114adc8419cbf2be90f512 by Yuri Chornoivan. Committed on 24/02/2018 at 13:01. Pushed by yurchor into branch 'master'. Add a note about LaTeX code in annotations M +5 -0 doc/index.docbook https://commits.kde.org/okular/fbd0fd69af1e4f6d10114adc8419cbf2be90f512