Is this registering to get an Abode ID at all, or getting the registration applied to the ebook.
To get an Adobe ID does not require any specific eBook (or any eBook at all, it is the same ID for all dealsing with Adobe).
Go to the adobe home page and try to sign in. You will be directed with an option if you don't already have an Adobe ID>
If you have an ID and want to get it the ereader authorized with it