I remember that with Zotero for iOS the zotfile functionality does not work for pointing to pdfs in iCloud, say
To install a plugin in Zotero, download its .xpi file to your computer. Then, in Zotero, click “Tools → Add-ons” and drag the .xpi onto the Add-ons window.
1. Attaching recently added files -- I don't think this is getting a ton of use, but I've definitely had projects where that's been quite useful. Seems maybe a bit tricky in terms of UX, but non-contentious feature-wise
Upload image file with the file dialog or by dragging and dropping images onto the dashed region