Do I need to register with Adobe?
If you decline to register with Adobe, your digital content is not associated with your personal account, but with the device you use to download the e-book. This prevents you from backing up or transferring your e-books to other devices, such as your e-book reader.
At www.adobe.com/de/, click "LOGIN" in the upper right corner if you don't already have an Adobe ID. Select the option "Not a member yet? Create an Adobe ID" to register your personal Adobe ID free of charge.