Hi!
Thanks for the reply. I followed exactly the process explained here
http://blog.calibre-ebook.com/2017/0...port-your.html
When I picked an empty folder to import in, the process seemed to go fine, calibre restarted by itself so I thought that once the software started again I'd see a full library, but in the software itself, the library was empty (the folder is full of all my books in folders named by author). That's why I thought I had to "add" my books", but though the books were added in Calibre, the metadata didn't so they weren't classified by collection (collections I had created).
I still have my backup file titled "part-0001.calibre-data" like in the example on the website I found. I tried doing it a second time but the same thing happened. I really don't know what I'm doing wrong.
Marie