If you only just now overwrote it, it will be complete preserved in the file
called "Backup of [fn]". If, that is, you enabled "Always create backup
copy" under Tools-Options-Save.
Sometimes you can find a document in the detritus of the the temp file
directories. Don't give up if you search the contents of all files on your
drive for some characteristic string in your lost document. I am pretty
sure that Explorer will not search the temp file directories. You may have
to go directly to those subdirectories or, if you've enough room on your
disk, copy them to a new directory outside of the Windows directory and then
search for that unique content. (I emphasize content because the temp files
in the aforementioned temp directories will have weird names unlike [fn].)
I don't know if that "fools" Explorer into letting you search such a "new"
directory and its subs. You'll have to experiment with that, say, by saving
a file to one of the subs that you create that has something like "Thank
goodness John Kerry wasn't elected Presidentxyz" and then seeing if Explorer
picks it up.
Word's document search utility is pathetically obtuse and woefully
unreliable in my experience, so I advise you not to go there. Then again,
it could just be me. No se.
I think searching in the Command Prompt window using DOS search capabilities
may also be subject to the same limitation as Explorer. "DIR fn.doc /s"
picks up, from the root directory, files with the name you specify. I think
DOS would allow you to search file content as well but I surely do forget
most of those commands.
Last ditch, search for "file recovery" on Google and go crazy.
Richard