Windows operating systems have the MS-DOS command prompt that allows you to manipulate—copy, delete and rename—files. In Linux, such commands are available via a terminal window. The way to change the file extension in both Windows and Linux is to rename a file providing the new extension.
In Windows XP/Vista
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Step 1
In Windows XP/Vista, click "Start." Click "Run" (only Windows XP). Then type "cmd" and press "Enter" to open the command prompt window.
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Step 2
In the MS-DOS shell window, type "cd c:\path\to\file" and press "Enter." Example: cd c:\user\test. If the designated file is on a different logical drive (e.g., on drive D) type "d:" and press "Enter." Then type the "cd" command as above.
Step 3
Type "dir" followed by "Enter" to list the directory content and find the designated file.
Step 4
Type "rename filename.ext filename.new" and press "Enter"; ".new" is the new file extension ("filename.ext" stands for any file you might have; for example: rename report.txt report.doc).
In Linux
Step 1
Right-click on Desktop and choose "open terminal" from the pop-up menu.
Step 2
Type "cd /path/to/the/file" followed by pressing "Enter" to navigate to the directory having the file. Example: cd /home/tom/doc.
Step 3
Type "ls .ext" and press "Enter" to list all files with the extension "ext," and confirm the file exists in this directory. For example: ls .txt.
Step 4
Type "mv filename.ext filename.new" and press "Enter" to change the extension. For example, mv report.txt report.doc.