I downloaded Adobe Digital and a library book. The Nook icon won't show up on Adobe library. Book is on my Nook, but can't open it. Error message of incorrect user name/password.

I downloaded Adobe Digital, got a user name and password.  I downloaded a library book, which shows up on the Nook Library, but the Nook icon won't show up on Adobe Library. I dragged the book to the SD card on my desktop computer.  The book is on my Nook, but I can't open it. Error message of incorrect user name/password. What do I do next? I'd like to read the book.