How To Fix File Extension Error While Renaming

Error Message:
Rename: If you change a file name extension, the file may become unusable. Are you sure you want to change it?

Translation:
A reader likes to create text files by right-clicking the Desktop, clicking New, and then clicking Text Document. When he tries to rename the text files, the above error messages appear. The reader has the same problem when trying to rename graphic files or any other files. The reader noted that he was able to fix the error by reinstalling Windows.
Solution:Many Windows users know what file extensions are, but few understand how Windows handles the three-character extensions, such as .DOC (Microsoft Word document), .RTF (Rich Text Format), or .TXT (text file). As far as Windows is concerned, it doesn't matter what extension is appended to a file. The extension tells the OS (operating system) what program to use to open the file.
For a quick demonstration of how this works,

Create a TXT file using the procedure the reader used, open the file, type some text, and save the file. Look at the icon for the file and if the .TXT extension displays, right-click the icon, click Rename, and change .TXT to .RTF. Now open the file. Depending on the file associations you've established, the newly minted RTF document opens in either your word processor or WordPad, and the text you typed is still there. The contents of the file haven't changed, but the program used to handle the file and the formatting used for the text has changed, just by typing a new extension. Now try changing the .TXT or .RTF extension to .BMP (a bit-mapped graphic). The icon changes to that of a BMP file, but when you try to open the file, either nothing happens or you get an error message. The exact message depends on the program your OS uses to open BMP files. That's because the document contains text and not graphics information, so the graphics program that would normally open an image file can't read the data. Here's a related problem: If Windows is configured to display file extensions and you rename the file without typing an extension, Windows can't do anything with the file. There's no extension, so Windows has no idea what program to send the file to when you try to open it. What does this have to do with the reader's error message? Well, the message above isn't so much an error as it is a warning: Windows is asking if you are certain you want to change the file extension.
There are two ways to handle this situation. If you want Windows to display file extensions, note the extension whenever you rename a file and be sure to type it in. For example, if you rename a file called Old.txt, make sure you type New.txt and not just New. If you don't want to deal with extensions at all, configure Windows to hide them. Double-click My Computer, click Tools, and then click Folder Options. In Windows 95, open the View Menu and click Options. Now select the View tab and scroll down the list until you see an option that says Hide Extensions For Known File Types and put a check in the box next to that entry. Click Apply and the extensions disappear from all of your files. Now you can rename anything without typing an extension, and Windows will automatically retain the extension that existed before you renamed the file. The reason reinstalling Windows solved the problem for the reader is that Windows defaults to the hidden file extension settings when it is installed.