Zotero allows you to share collections with others by creating either private or public groups with associated libraries.
If you set-up automatic syncing between Zotero Online and the Zotero desktop app, this new Group Library should automatically appear in the Zotero desktop app. If syncing is not automatic, open the Zotero desktop app and click the Sync with zotero.org icon.
Please visit Zotero's documentation page for more information.
References can be included in multiple collections or sub-collections.
Tags are keywords that allow you to describe an item. You can add multiple tags to a single reference.
Duplicate references are those that have been added to the same Zotero Library more than once. Items added to more than one Collection are not considered duplicate items.
All annotations are stored within this copy of the PDF.