How to show filename extensions

By default, Windows doesn't display filename extensions. They're there, you just can't see them. An extension is the three-character suffix at the end of a filename. The extension tells you the file's format. For example, the filename Employees could be anything. Displaying the extension gives you instant knowledge: Employees.doc is a Word file; Employees.mdb is an Access file; and so on. The following lists contains the most popular Office application extensions:

  • Word: .doc
  • Access: .mdb
  • Access Project: .adp
  • Excel: .xls
  • PowerPoint: .ppt
  • Outlook: .pst

Seeing extensions might not matter most of the time. Windows and Office make it easy to work in extension ignorance. You double-click a file and Office knows which application to open. You don't need to know a file's type to use it.

Unfortunately, not all files are bearers of benign information and good will. Viruses, Trojans, and other evil stuff carry information bent on destruction. Of course, you should have antivirus protection, and I'm sure you update it often, perhaps even every day. The sad truth is, every day a new virus strikes somewhere. No antivirus protection guards against all viruses all the time. That's why extensions are important.

Let's suppose you receive a file named Employees as an e-mail attachment. You don't know what type of file it is, but you just updated your virus protection software, so you know it's safe, right? You double-click it, and your computer world goes dark.  Okay, now that's a bit macabre, but play along for a moment.

Let's replay that moment. This time, your system displays extensions and you can see the file's full name is Employees.exe or even Employees.doc.exe. (The last extension is the only one that matters.) Would you open it? Most likely, you wouldn't. You'd verify its contents by contacting the sender if you had any doubt. The .exe extension is particularly dangerous because it's an executable file. That means it contains instructions that Windows runs when you double-click the file.

I recommend that you display extensions. Fortunately, it only takes a few steps:

  1. Choose My Computer from the Windows Start menu. (You can use any method for launching Explorer.)
  2. Choose Folder Options from the Tools menu and click the View tab.
  3. In the Folder Options dialog box, uncheck the Hide Extensions For Known File Types option.
  4. Click OK.

Now, you might be wondering what all this has to do with Office. Once you display extensions via Windows, Office will display extensions as well. For example, the Filename and Save As Type  controls will display the filename and the extension, as shown below. Notice that this Word filename now displays the .doc extension, and the Save As Type control also displays .doc. When you enter a filename, you don't have to include the extension -- Office will continue to take care of that for you.