Adobe ACROBAT READER 7.0 Manual page 232

Upgrading Digital Editions
If you owned and read Digital Editions using an earlier version of Adobe Reader, you
need to migrate these files to Adobe Reader 7.0. The first time you open My Digital
Editions bookshelf or try to read a Digital Edition using Adobe Reader 7.0, you are
prompted to migrate files. Follow the on-screen prompts.