tags | Draw a rectangle, highlight an area

Tools -> Review (F6)

Works in okular 1.3.2, Debian Buster.

 % dpkg -l okular | grep ^ii      
ii  okular         4:17.12.2-2.2+deb10u1 amd64        universal document viewer

Ref:-

• http://docs.kde.org/stable/en/kdegraphics/okular/annotations.html
• https://superuser.com/questions/349000/how-do-i-annotate-a-pdf-file-in-ubuntu