Why do I need and Adobe ID?

Why do I need an Adobe ID?

All books with DRM protection are linked either to computer to which they were originally downloaded or to Adobe account.
If Adobe ID is not entered when installing ADE, all the purchased books will only be available for reading on this computer (where ADE is installed). You may not transfer them to another reader, they may not be recovered from a backup copy if the operation system is reinstalled. Any data failure may result in the need to rebuy the book. Availability of six Adobe ID allows copying the book to 6 computers and/or mobile devices and gives an opportunity to recover the previously purchased books from a backup copy.

Please note: if you have purchased books from a computer with installed ADE not authorised with Adobe ID, after entering Adobe ID, all previously purchased books nevertheless may not be transferred to another computer or reader. Username (Adobe ID) and password entered upon registration must be entered during installation or after start (if the software has been already installed) of Adobe Digital Editions.