Some of us old-timers still go to libraries.
However, in the 21st century we can also go to electronic libraries.
The vast "OverDrive" ebook library system uses ACSM files. When you go online and "borrow" a library book, the ACSM file links the book to your library account, then you can download the actual ePub. When the loan time expires, DRM kicks in and the book is no longer readable.
OverDrive, Adobe and ACSM have been working well together for many years.