Some books are authorized using your Adobe ID (as used on the Adobe website);
it is best to get one (you probably have one to use this forum) and register ADE even if you don't actually need it immediately.
Some vendors use the Adobe system but their own vendor ID rather than the Adobe ID. Not sure about Kobo.
If the Adobe ID doesn't work, contact Kobo to check what kind of ID they need.
Some vendors use the email contact they have for you as ID, and the credit card number as password.
You may need your computer signon to install ADE (because of security), but it won't be the one to use for authorization once ADE is running.