e_adept_document_type_unknown -- Google Play Books

As we do not seem to get any answers from Adobe, and the software and entire Amazon/Adobe based DRM eco systems might best be considered abandonware, I would just like to pitch in that the best way to stay out of trouble is to not use outside sources for book purchases meant for the Kobo readers or other readers. Avoid everything that means using an Amazon or Adobe based DRM, try to buy books, if possible, directly from the native shop for your specific reader and if possible, buy DRM-free to begin with.

I tried to solve this with Adobe, Kobo and also with Google. When Googles techs gave up on it, Google were kind enough to actually give me a full refund for the book I bought on Google Play.

I think that was fair enough, as I was then able to buy the book directly from the Kobo Store. Now, I know that the Kobo store isn't nearly as well stocked as Googles or Amazons (this thing happens with some books from Amazons Kindle store, as well - converting them turns out to be impossible). But I'll try and actually convince Kobo and publishers to add books in future, rather than support eco systems that are obviously not working as one would imagine and expect. Hoping, still, for a solution from Adobe on this, but not holding my breath, sadly. I would have wanted to see Adobe do more, and I look forward to the day when they do. In the mean time, I don't see any other option than to abandon their software and eco system entirely. Which is a shame.