Changing the file extension in Windows is tricky if you cannot see the extensions. Generally, changing file extensions is not advisable, because if you change the extension to something that Windows doesn’t understand, you’ll be unable to open the file with its default or alternate program(s). Also, changing a file extension doesn’t necessarily change the document type, and the file data could become garbled if you change the extension.

If, however, you’re sure you know what you’re doing and you want to change a file extension, you can do so easily. The first step is to make the file extension visible. Open a folder, go to View, Folder Options, click the View tab, uncheck the Hide File Extensions For Known File Types box, and click OK. Then you can change a file extension by right-clicking on it, selecting Rename, and changing the three letters of the file name that come after the dot.