[moved to the Adobe Digital Editions forum]
Currently, Adobe Digital Editions is not available for iPad/iPhone.
So how do I return library bookS that are downloaded PDF format? Overdrive suggests using digital editions.
Overdrive does have an iOS app for iPad/iPhone. I'd recommend visiting the OverDrive Help website for further assistance.
You can also use the desktop version of Adobe Digital Editions on your Windows or Mac desktop/laptop computer to return library books.