Not totally sure why we don't allow this, but I guess we should — as I say there, we do allow it on iOS, where PDF metadata retrieval also isn't available. Here it's a bit more likely to just be a mistake, but I'm not sure that's a reason not to support this one feature when we support other things.
https://forums.zotero.org/discussion/101314/zotero-connector-not-saving-pdfs
Not totally sure why we don't allow this, but I guess we should — as I say there, we do allow it on iOS, where PDF metadata retrieval also isn't available. Here it's a bit more likely to just be a mistake, but I'm not sure that's a reason not to support this one feature when we support other things.