When I select the words in PDF and do copy, paste, wherever there is "f" it always shows "?" and the letter that close to "f" is also missing. This problem not only shows when I do copy-paste but also shows when other software is extracting information from my PDF document. Can anyone tell me what's wrong?
Sounds like those could be ligatures.
Thanks. I just realize this only shows on the PDF I generated using Letax. Is there any idea on how to resolve it?
Update: Problem solved after disable ligature function in my latex.