I just started using Zotero. Before I consequently used JabRef, Mendeley, cb2bib, and Kbibtex. Zotero is much better and more convenient and has all functions which I need. I stored bib files in a separate folder and made "keep updated", and all pdf files of papers in another separate folder. In Zotero I made the links for these pdf files but nevertheless, many empty folders appear in Zotero/storage/. One folder is for one pdf file. May I delete them? I have a great library and therefore have a great number of empty folders. Maybe Zotero keeps them for its internal needs?