[GeoffR]

Kobo devices don't come with ADE as such, they come with an epub reader based on Adobe's RMSDK. The features of Kobo's epub reader don't necessarily correspond exactly to any particular version of ADE, because there are a lot more versions of the RMSDK than there are versions of ADE. I think the closest would be ADE 3.0 since that was released at around the time the Kobo firmware last updated the RMSDK.

I don't know exactly which version of the RMSDK is used, but it was last updated to one of the RMSDK 10 versions in firmware version 3.5.0, and it hasn't been updated since. i.e. the RMSDK in firmware 3.13.1 is exactly the same as the one in firmware version 3.5.0.

Edit: Beware that if you use ADE 3.0 you may receive books using the a new DRM scheme sometime in the future, and once you receive a book in the new scheme you probably won't be able to download it in the old scheme. So if removing DRM is important to you, dont use ADE 3.0 or later to download books.