highlighting a pdf in zetero

Hii, Recently I have been unable to use the highlighting function in Zotero. I used to be able to do it with ease, but now it seems like it doesn't recognise the text. I've tried different texts and some work and some don't. So I'm not sure if it has something to do with the format of the text or something in my settings.
I appreciate any help!
Sign In or Register to comment.