As mentioned, if the file's contents have been overwritten, then there's not much you can do.
You could try and find an earlier version of your file using data recovery software and performing a deep scan of your drive. This will look for data that is not tied to a file (i.e. an earlier version of your work).
You could try:
- Recuva: small and free, feature rich, gets the job done
- GetDataBack: not free, but highly effective (I've used it in the past, was quite satisfied with the results)
- There's also a wikipedia article on data recovery software here, where you can check many other options