DRM (Digital Rights Management) is intended to prevent from unauthorized use. To put it simply: it means you can’t freely share the ebook file you bought. No matter how insane it sounds, we have to live with that.
The Adobe system is being used by Barnes & Noble, Kobo, Google, and Sony. Ebookstores in many countries also use it, as it’s more affordable than developing a native file protection system.
…There are two ways to deal with Adobe DRM: either remove it or accept it. The third option, ignoring it, doesn’t pay at all.
…And while DRM as such is a huge limitation, if you wisely handle it, you can be more flexible in where you buy books, how you store them, and who can access and read them.
… First of all, get an Adobe ID. Secondly, authorize with it any of the devices you would possibly want to use to read ebooks. Do it before you download the first ebook. Here is a tip on how to authorize a computer and your mobile devices with Adobe ID credentials.

Mer info pa http://ebookfriendly.com/2012/03/06/what-is-adobe-drm-and-how-to-deal-with-it/