Change the filename extension when file renamed

Note: Typically, you should not rename a file by replacing the extension, as this can make the file unrecognizable to the program that created it. For this reason, when you try to change a filename in Windows, you will probably see a warning message.
In Windows, you can usually change a filename's extension (e.g., .txt or .doc) by simply renaming the file with a new extension, but this may not work under certain conditions.
Sometimes the new file extension is added to the name of the file in front of the old extension, and the old extension stays the same (e.g., myfile.doc.txt) .

Right click on the file and go to "Rename." If you can't see the extension, go to "Tools", "Folder Options", "View" tab and uncheck "Hide extensions for known file types."Answer: