So lately I’ve been plagued with a bug where fi and fl ligatures are not displayed in Okular. Needless to say, this makes reading textbooks, especially mathematics textbooks with all those words like “define” and “definition”, supremely annoying.
After finally having some free time, I started googling around and finally found the cause. It’s a bug with poppler.
Fortunately, there is a workaround that solves the problem. Hopefully this bug will get a properly fix soon, but for now this will do.