When I import a PDF into Zotero, does Zotero save a duplicate of the file, or link to the original? I'm wondering if I can delete the PDF that I downloaded. Thanks!
If by "import" you mean "drag to Zotero" then yes, those files are duplicated. (FWIW, wherever possible using the Save to Zotero button on an item/abstract page is the better option and will normally attach the PDF if you have access, see https://www.zotero.org/support/adding_items_to_zotero#via_your_web_browser
Upgrade Storage
(FWIW, wherever possible using the Save to Zotero button on an item/abstract page is the better option and will normally attach the PDF if you have access, see https://www.zotero.org/support/adding_items_to_zotero#via_your_web_browser