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

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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 under certain conditions this may not work.

Sometimes the new file extension is added to the name of the file in front of the old extension, leaving the old extension the same (e.g., myfile.doc.txt) . To fix this problem, see ARCHIVED: In Windows or Mac OS X, how do I reveal file extensions?