I belong to two local critique groups and sometimes do other critiques for friends or writers I know online. Most of these are done on the computer rather than on a printout. Since standing at my computer is not particularly pleasant for reading long things, I prefer to crit on my iPad.
However, the word processors on iOS mostly don’t have track changes, so I have to spend time back at my computer finding all my inline comments and turning them into “real” comments, and it’s also a pain to mark grammar and wording changes.
Several weeks ago someone pointed me to Doc^2 HD. It supports track changes!
So far it’s worked wonderfully. The track changes functionality is fine; I haven’t had any trouble opening the edited files in Word. I’ve had a few problems when it refused to open a file (it connects to Dropbox) and once it refused to save, although when I closed and reopened the app, it had in fact saved. This could obviously be a problem but I simply save obsessively and haven’t lost anything yet.
My only complaint is that it needs an internet connection to get at the files in Dropbox; you can’t tell it to download them so you can edit them offline later. Since I do most critting at home this isn’t a big deal, but if I wanted to also do my writing in this app it’d be a dealbreaker.
If you need something that will let you track your edits or comments, this does the job quite well.