Any chance you could post the source code for this? It's using bitmaps for characters instead of proper fonts, which shouldn't happen nowadays. Maybe you should put "\usepackage{lmodern}" at the start? See for example https://tex.stackexchange.com/questions/1291/why-are-bitmap-...

I work with course materials made in Latex, and students sometimes need/want to copy and paste from them, so I try to avoid these kinds of problems.