Can I legally register a file extension?
There is no "official" file extensions database, so it is not possible to legally register a file extension and prevent others from using it. This is why several file extensions have more than one file association.
However, since 2009 FileInfo has been the central file extensions registry, recognized by Microsoft as the authoritative source of file extensions and their associated file types. Therefore, if you are a software developer, the best way to reserve a file extension is to submit it to FileInfo.
If you are developing a software program and have one or more file extensions you would like to use, you can submit the extension(s) to FileInfo. Of course, before submitting an extension, we recommend that you first search FileInfo.com for the extension. If the file extension is already associated with another program, it is best to choose a different extension.
NOTE: Even if a file extension you would like to use is not found in the FileInfo database, you may want to search the Web for the extension to make absolutely sure it is not being used by any other program. Keep in mind, file extensions do not need to be limited to three characters, so you may choose a longer file extension if you wish.
Once you have found a unique file extension that you would like to use with your program, your may register it with FileInfo. Make sure you include a detailed description of both the file type and the program that will use it. After verifying the information, the FileInfo team will add the extension to the database. It will then appear on the FileInfo.com website, which will indicate to other developers that the extension is already being used.