Import data is read on your device. To find matches, the app sends titles, authors, and ISBNs to its server, which queries book catalogs. Importing is therefore not an entirely offline process.
Before you confirm, reading statuses, ratings, dates, reviews, and highlights stay on your device. Once imported, these records become part of your library and sync if you are using an account.
Confirmed books may contribute public details to the catalog, such as title, ISBN, cover, and the identifier on the source site. Your reading statuses, personal ratings, and notes are not part of that catalog contribution.