If you download the .pdf, your book can only expire; more specifically you cannot return it early. However, if you use Libby, you can return the book early or renew directly from the application. Simply touch “shelf”, “loans”, “manage loan” and the action you want to take (renew, return). Libby also allows you to have more than one e-book available on your device, and you can toggle between them (reading more than one book). On long trips where WiFi isn’t always available, I often have several books on my device (using Libby), and return them as I finish.
I believe e-books are returned automatically, i.e. they would disappear from your e-reader.
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