DRM is the method e-book providers use to prevent copying, sharing, or to limit the amount of time you can download a book. It is different from the file format and set by the site where you download the e-book.
Different e-book providers use different DRM schemes which can limit which device you can use.
Common DRM schemes:
- Adobe Digital Editions (encoded PDF)
- Amazon (Kindle or Kindle apps)
- Apple iBooks (iOS only)
- Barnes & Noble (Nook)