Can't copy PDF text in Preview

It started a few weeks ago where I noticed I couldn't copy text from PDF's. If I did an Export as PDF and just save over the original file then copying worked for awhile but now not even that works. I've looked around for an answer but the only thing I've found is about changing the colour of the highlight in the System General Preferences, but that didn't solve anything for me. I can highlight and select Copy but nothing seems to get stored in the Clipboard other than blank space. Even pasting it into a plain-text or rich-text document just gives me a field of blank space that can't be altered in any way (so no choosing a text style or colour).

Anyone know what the hell is going on with it?