A file name extension is a set of characters added to the end of a file name - normally after a full stop '.' with 3 x characters such as '.doc'. This determines which program, or application, should open it.

Follow these steps to choose whether Windows displays these file extensions.

In Microsoft Windows Vista or 7:

• Open Folder Options by clicking the Start button, clicking Control Panel, clicking Appearance and Personalization, and then clicking Folder Options.
  
• Click the View tab, and then, under Advanced settings, do one of the following:
  
  • To hide file extensions, select the Hide extensions for known file types check box, and then click OK.
    
  • To display file extensions, clear the Hide extensions for known file types check box, and then click OK.
    

• Open Folder Options by clicking the Start button and clicking File Explorer.
  
• Go to the folder with the files you would like to show the extension.
  
• Click the View tab :
  
  • To unhide file extensions, tick File name extensions.
    
  • To hide file extensions, untick File name extensions.