Thank you Boris!

To recap, the eDGe need to be registered first, and the email you use during the registration for Entourage and Adobe should be the same as the email you use for purchasing Adobe Digital Editions ebooks. At least the Adobe account (during registration on the eDGe) and the email your using for the purchase Adobe Digital Editions must be the same.

Does it mean Adobe Digital Editions is DRM protected by the email you use? Am I allowed to read this ebooks where ever I use the correct Adobe account, PC, eDGe, others?

Not protected PDF ebooks/documents can be read anyway on every device including the eDGe.