And like any new app, it could use some work. In spite of its name, Adobe Digital Editions 4.0.2 for the iPad is very much a beta release of the app.
It offers the same Epub3 support found in the Adobe DE4 app which Adobe launched last fall for Windows and OSX, including rich layouts and embedded audio and video. From the mentions of support for interactive quizzes, and math formulas, it looks to be Adobe's bid to enter the nascent digital textbook market.
The app doesn't have much in the way of features yet, but there's a search function and a timer which will tell you how long you've been reading. Readers can bookmark, highlight, or look a word up in the dictionary. There are optional dictionaries for a wide variety of languages from English to Russian to Thai.
The app doesn't offer many formatting options, but it does let you change the font size and margins (in Epubs). It also has 5 color themes (including white, night, ivory, sepia, and blush):
I've been testing the app for a few minutes this morning, and it is rather slow and clunky. It works, but this wouldn't be my preferred app (even if I hadn't caught Adobe spying on users several months back).
But if you use Adobe DE 4.0, you might want to install the app. There's been some speculation that Adobe's spying activities had been intended to function as a syncing service which would let Adobe DE users share an Adobe account across multiple devices - PC and iPad.
Most of the major ebook platforms offer this kind of sync service, and it would make sense for Adobe to add a similar service. And since it would be useful to some readers, this app is worth a look.
But I also don't see a way to enable that sync, nor is it mentioned as an option at this time. So there's really no need to rush out and install the app.
You can find the app in iTunes.