Although modern operating systems such as Windows Vista and Mac OS X are designed to deliver a neat, streamlined interface, the absence of file extensions can sometimes be frustrating. Without the knowledge of the file extension, it is sometimes difficult to know whether a file is to be opened in an office program, is an executable program, is an archived file or one of the numerous other standardized file extensions. Just a few clicks of the mouse, though, can quickly and easily reveal this information.
On a PC
Find the file. If the file you want to find is on your desktop, simply move the mouse pointer to the file. If the file is somewhere else on your hard drive, though, first click on "Start" then select "Explore." Click on the folder where the file you want to identify is stored, then move your mouse to point to the file.
Click the right button on your mouse to bring up the special menu.
Select "Properties" at the bottom of the menu. Selecting this option will reveal the full file name, including the extension.
On a Mac
Follow the same process as described in Step 1 in the PC section to find the file.
Hold down the "Command" key, and click on the file in question. If you are using a two-button mouse such as those designed for PC users, you may also right-click on the file to access this menu.
Select "Get Info" from the command click menu. The extension of the file will be displayed under the "Name & Extension" section. From the file information display, you may also check or uncheck the "Hide Extension" option to display the file extension along with the file name.
Be wary of files ending in .exe. These files are executable programs on a PC and, if not from a trustworthy source, may damage your computer. Although most software (including name-brand products such as Word, Excel and Dreamweaver) are saved as .exe files, an executable file from an unknown source or received through unsolicited email may contain a virus. Files with the extension .exe will not run on Mac OS X.