DRM (digital rights management)

DRM (Digital Rights Management) encrypts the file so it can only be read on an authorized account or device. Amazon Kindle applies a proprietary DRM by default; other platforms (Kobo, some independent bookstores) let the author choose to sell DRM-free.

DRM protects against unauthorized sharing, but it also complicates legitimate multi-device reading and can put some readers off. Many self-published authors deliberately choose DRM-free to favor the reading experience.