If you try to open an Amazon purchased ebook on a device that is not registered to your Amazon account it will give you an error message referring to Digital Rights Management. There is a workaround using Calibre allows you to remove the DRM and change to file format.
When you buy an ebook on Amazon, you don’t own the book. You bought the right to read the book on any electronic book reading device that is registered to your Amazon account. The book is encrypted with Digital Rights Management. There are software programs that can remove the DRM, but it’s probably illegal. BAEN ebooks are sold without DRM.
It could be smallpox and measles and earthworms day on one side and syphillis potatoes corn tomatoes and tobacco on the other side, though I think I saw a documentary that said that Egyptian mummies had syphillis and were embalmed with tobacco. Those Phoneesian traders really got around. The more you learn the less you know.
Proprietary thingies make more profits for the manufacturer. Capitalism at work.