Saving a file only with extension

I was trying to create an OpenXML package manually. For that, a file named ".rel" (only with .rel extension) needs to be created. But if generally if we try to rename a file only with extension we will be getting the message "You must type a file name" and we can't rename the file.

There is a workaround to get rid of this problem. Instead of renaming the file, open the file in NotePad. Use the "Save as" option and type only the extension name in the File Name box. It will be saved only with the extension.