Ugly but functional
The interface needs a general face-lift but this is the only app I know that can retrieve a text file from Dropbox, edit it then save it back. It is also the only one that can do the same while being called from within Dropbox, which is very versatile. Neither Apple Pages nor Microsoft Word can do that. (Word opens doc files but not simple text files, mind you).
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Docs To Go Premium, v5.2.7