I'm sure that there are lots of apps that do this. Lots of people like goodreader, and it previews lots of file types. I use textastic for this sometimes, since I look at code a lot, which of course is text. It supports sftp and webDav and dropbox, but the file can be any type, not just text. You can then "open in" whatever other app will take the file type. Which, of course, leaves an extra copy to delete. File management on the iPad is kind of a pain, but it works. Probably you already knew about the pain in the butt part.