There are two types of Adobe DRM for ebooks - the one that uses your cc number (think the call it "social" drm, used by B&N) and the one that is tied to an Adobe ID(uses your email address to register, used by kobo, google, overdrive (libraries) and sony.
If you dont have an ADE (Adobe Digital Editions) id yet,go to their site and create one. (Two notes: Think there is still a limitation as to the number of devices/apps that can be registered to a single id. "Think" it is 5 or 6. Registrations can be reset, but you need to be aware of this. A long time ago (in ebooks, 2009), the email address used to buy your books had to match the email account used to create your ADE account. Dont know if thats still true or not.)
Once you've gotten your ade id, on the HD devices, you go into Settings and register/set up your id. And then sideload the book and you can read it. (Other nooks models can be registered too, but it involves downloading ADE onto your computer, registered the program, and connecting the nook to register it.)
I use the Kobo app to download and read Kobo ebooks on my Nook HD. I also have the Kindle app to do the same with Kindle books. I'm pretty sure B&N didn't know what they were doing when they made these devices full Android tablets.
Let me see if I've got this right. I can read any Kobo book directly on my HD+ so long as I have purchased the Android version of the book?
Be still my beating heart! Thanks.