Checking details from
http://download.kobobooks.com/learnmore/touch_userguides/Kobo_eReader_ Touch_User_Guide_110922.pdf
and going back to your original post, I notice on page 26: You can’t add DRM-protected books using a microSD card
I don't know why it has that restriction, but unless that guide is out of date it seems fairly clear you can't do what you want.
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Going on to the second post ...
When you factory reset the Kobo you probably lost its registration/authorization.
It must have been previously authorized, or it would not have been able to read the DRM ebook.
You current computer must be correctly authorized at the moment as you would not be able to read the DRM book.
You should be able to copy authorization to the Kobo using the menu/Help/Authorize Device command to ADE with the Kobo connected.
(Library/Authorize device on the older more reliable ADEv1.7.2)
(see Adding books using Adobe Digital Editions on page 27 of the manua above)
DRM free EPUBS are easily handled and are not an issue.
As an aside, if you use these for most of your reading,
I suggest you use Calibre (http://calibre-ebook.com/) rather than ADE as it is much better in almost every way (except it can't handl DRM).