Format or delete C drive with using Command Prompt (CMD). This allows you to remove all data and reinstall Windows 11/10.

The Windows 7 System Recovery Command Prompt is a text-based console that allow you to perform maintenance and recovery tasks on your computer by typing the commands that you would like to execute ...

However, if your business needs to remove the file extensions, using the command line and a batch file is much faster than renaming each file manually.