You didn't specified what file format do you expect to work with.
I've tried
QuickOffice and
OfficeSuite, supporting doc/docx documents and they are working well on T1... but a bit slow for editing.
You may also try
Jota Text Editor which specialises on longer text files.
There's simple text built-in editor in
RootExplorer (only plain text).
Personally I didn't find comfortable to edit texts on common b&w eInk readers, except short comments or some handfree drawing.