In Windows XP or later, why can't I change the filename extension when I rename a file?

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) .

To fix this problem:

1. From the Start menu, click Control Panel.
   
   
2. From the Control Panel, open Folder Options.
   
   
3. In the window that appears, click the View tab.
   
   
4. Uncheck Hide file extensions for known file types and click OK at the bottom of the window.
   
   

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