A simple batch file to get you started.

Copy and paste this sample code into notepad and save the file with the .bat extension.

ren *. *.doc

Should you put this batch file into a folder containing numerous files that were saved without the .doc extension and double-click the batch file, it will add the .doc extension to all of the files without extensions.

This is a simple batch command that was useful when I presented the solution to one of my coworkers.

My coworker took a call from the helpdesk in which one of our users had this problem.  I provided the batch file to the tech that took the call and he was amazed that it solved the problem, avoiding having to individually rename all of the files that weren't associated with Word due to the lack of extension.