Question about zotero, I just started using it and I can’t seem to find a way to direct it to PDFs I have already downloaded? Is there a way to do that or does it only have the PDF finding feature?

You can just drag and drop PDFs. Either to the list to create a new item or to an existing item if you already have it there.

Also, is there a way to make it always use the classic interface when adding a citation? I keep having to click “show classic interface” or whatever the button is, and it’s a tad annoying.

Zotero: Edit: Preferences: Cite: Word processors: Use classic Add Citation dialog [X]