How To Display File Extension Names

Files in Windows have an extension name which indicates what type of file they are and therefore which program should be used to open them. A file extension is usually a dot (.) followed by 3 letters after the filename.

E.g. for a file called resume.doc the file extension is .doc (indicating a document typically opened by a word processor). Unfortunately, extensions for known file types are hidden by default in Windows – so if you had stored a resume.doc file in (My) Documents you would see it displayed as just resume not resume.doc

Is Hiding File Extensions A Problem? Yes. there are 2 problems:

1. It is a security risk. Let’s say someone creates a malicious program which will infect you with a virus if you open/run the program. They name the file ‘interesting.doc.exe’ which just means the filename is ‘interesting.doc’ and the extension is .exe

If you see the whole thing you can tell immediately (from the extension at the end) that it is a .exe program (executable), not a .doc Word document. This should alert you that it is likely to be a virus program and you should not open it.

However, if you have extension names set to hidden (the default in Windows), you would only see the filename as ‘interesting.doc’ – because .exe is a known extension type and is therefore hidden from you! In this case you might well open it thinking it is just a document. Thanks for nothing Microsoft!

2. You may need to know the file extension. If you receive an error message saying that Windows cannot open a file, it is possible that you do not have a program capable of opening it. To find the right program you need to know the file extension name.

How To Unhide File Extensions In XP

  • Click Start, then click My Computer to open the My Computer window.
  • Click ‘Tools’ in the menu bar then click ‘Folder Options’ to open the ‘Folder Options’ window.
  • Click on the ‘View’ tab, scroll down the Advanced Settings and untick the ‘Hide extensions for known file types’ box.
  • Click the ‘Apply’ button and then OK to close the Folder Options window.

How To Unhide File Extensions In Vista and Windows 7

  • Click Start and type ‘Folder’ into the Search box.
  • Click on ‘Folder Options’ in the top (Control Panel) section of the search results to open the ‘Folder Options’ window.
  • Click on the ‘View’ tab, scroll down the Advanced Settings and untick the ‘Hide extensions for known file types’ box.
  • Click the ‘Apply’ button and then ‘OK’ to close the Folder Options window.

File extensions will now be shown for all filetypes.

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