When I download a book from the library, it shows up in my Adobe library but when I transfer it to my Kobo Touch, a message shows up that says it can't be opened because it isn't currently authorized for use with my Adobe ID. It wants me to sign in with my authorized Adobe Id and try again. How do I do this?
You must first authorize ADE (digital editions) with your Adobe ID ... the one your registered at the Adobe web site.
The copy the authorization to the Kobo
You should now be able to copy the book to the Kobo and read it there.
Unfortunately both Adobe and Kobo have quite a lot of ways of making things not work; post back if you have more issues.
I tried this and it didn't work
Can you please give more details: what steps you managed and did work, what step you were at when it failed, and the symptoms (eg message) of failure?