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3.1. Making File Extensions Visible

What is a file extension?

Nearly all files in Windows have a "file extension", usually three or four letters after a dot. For example, a file called MyModel.xlsx has a file extension of XLSX. The file extension tells Windows what program to run when you double-click the file — for an XLSX file, that's Microsoft Excel. Most Windows installations are pre-configured to hide the file extensions, so a file actually called MyModel.xlsx would appear in Explorer as MyModel. You can right-click the file and select Properties » Details to see its full name, or look at the Type column in Explorer to find a description of the file type, such as Microsoft Excel Worksheet.

Why do I care?

Usually you don't. But you may need to send us a file of a type that your mailer rejects, or we may need to send you one. The standard way to do this is for the sender to change the extension to TXT, and the receiver to change it back to ZIP or REG or XLSM or whatever. If extensions are hidden, you can't do that, so you need a way to display file extensions.

How do I make file extensions visible so that I can change them?

In Windows 10 and Windows 8.1:

    1. Double-click This PC or any folder icon.
    2. Select the View tab of the ribbon.
    3. Check (tick) the File name extensions box.

In Windows 8:

    1. Double-click Computer or any folder icon.
    2. Select the View tab of the ribbon.
    3. Check (tick) the File name extensions box.

In Windows 7 and Vista:

    1. Double-click Computer or any folder icon.
    2. Click the down arrow next to Organize, and select Folder and search options. If you don't see Organize, press Alt+T, release the Alt key, and press letter O.
    3. In the Folder Options dialog, select the View tab.
    4. Remove the check mark from the box labeled Hide extensions for known file types. (It's a couple of lines below the first set of radio buttons.) Click OK.

In Windows XP:

    1. Double-click My Computer or any folder icon.
    2. In the menu, click Tools » Folder Options.
    3. In the Folder Options dialog, select the View tab.
    4. Remove the check mark from the box labeled Hide extensions for known file types. (It's just below the first set of radio buttons.) Click OK.

Additional keywords: Change file extensions, edit file extensions, filename extensions

Last edited: 2016-02-26

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