Using Your Own File Extensions

By default, Excel uses an XLS extension for all workbook files. You can, however, control exactly what extensions Excel uses with your workbooks. (You may want to use a different extension if you are trying to hide the fact that the file is an Excel workbook.) If you try to use a different file name extension by including it when you save the file, Excel still appends the XLS extension. For instance, if you explicitly save a file as MyFile.mef, Excel will still save it as MyFile.mef.xls.

If you don't want Excel to do this, then simply enclose your file name in quotes when you save under a new name. Thus, you would use the name "MyFile.mef" (with the quotes) and that is the file name which Excel will use.

In addition, if you save a workbook with a different extension (not using XLS), then Excel won't show the workbook by default when you use the Open command. To see all your varied-extension files, you need to follow these steps:

1. Click on the Open icon on the toolbar, or choose Open from the File menu. Excel displays the Open dialog box.
2. In the File Name field, enter an asterisk, period, and your desired extension. For instance, you could enter "*.mef" (without the quotes).
3. Press Enter. The desired files should be listed in the directory.
4. Select the file you want to open.
5. Click on Open.