You cannot use ADE with Kobo Arc in the same way you use a dedicated eReader device. (see extracts from manual below).
Install the Bluefire app which will allow you to register and Abode ID and read Adobe DRM ebooks.
Copy books from the computer using Windows Explorer or Mac Finder.
Overdrive app will allow you borrow, download and read Overdrive library books.
Some people have problems authorizing the Overdrive app, though.
aside ... Pretty much the same applies to all general tablet devices; Android and ios.
As far as I know, there is no equivalent support for Windows RT ... you just can't use it for generic Adobe DRM eBooks.
DL Reader app for Windows RT http://apps.microsoft.com/windows/en-gb/app/dl-reader/0be254fa-1323-4bda-92fa-698fe502456c
If you’ve bought EPUBs from other stores, or found free EPUBs on the Internet, you can import them into your Kobo Arc from your computer. You can’t import all eBooks to your Kobo Arc Library from your computer desktop; you can’t add PDF eBooks orDRM_protected EPUBS.
The Kobo Arc doesn’t support Adobe DRM, so if you’d like to read library eBooks you’ll need to use the free Overdrive app, or another reading app supported by your library. You can get the Overdrive app and many other reading apps from Google Play.
Thanks for that. I finally deduced the same and now use Bluefire as you recommend.