I have the original issue. I got Zotero and followed the instructions. About 8 citations in, Zotero has rejected 5 different citations from being imported claiming that they were magically the wrong file type. Same source, same file type, now it does not work. There is something horribly wrong with this App. Does anyone know why the same method and source could just start being rejected on the premise it is "the selected file type" is not the right format or what not. Nobody mentioned PDF until later - ignoring the original inquiry.
What exactly are you trying to do? Where kind of file are you trying to import? Where did it come from?