Highlighter has stopped working on most PDFs

Hello, I can't use the built in Highlighter anymore on locally saved PDFs. It only works on PDFs that are properly scanned in and where i can actually select the words. 2 days ago, I was still able to basically use the highlighter on all PDFs and draw on them however I liked. I haven't installed anything new or changed anything. I also have tried to reset Firefox and reinstalled it. It's still not working. I would really appreciate any help. I couldn't find anything based on my problems.