As stated in the Zotero documentation, when an item is dragged into a group library, it is a separate copy, and any changes to it will not be reflected in the source library from which it was dragged. My question concerns attached files. If a colleague drags an item with a PDF attached into a group library that I am the owner of, is a copy of the PDF copied into my storage space? Or does the new item in the group library simply reference the existing PDF on my colleagues storage space. And similarly, if a third colleague was to attach a PDF to the new item in the group library from his/her desktop, where would this PDF be stored?