If a file does not appear to have a filetype extension, open the folder it is stored in and click on Tools from the menu, then Folder Options. Click on the View tab and un-tick Hide extensions for known file types.
.avi - video file. Open with Windows Media Player
.bmp - image file. Open with Paint
.cfg - configuration file.
.dat - data file.
.doc - document file. Open with Word
.exe - program file. Double-click to run
.gif - image file. Open with Paint
.htm - web document. Open with Internet Explorer
.html - web document. Open with Internet Explorer
.ini - text configuration file. Open with Notepad
.jpeg/jpg - image file. Open with Paint
.mov - movie file. Open with Quicktime
.mpeg/mpg - video file. Open with QuickTime
.mp3 - audio file. Open with Windows Media Player
.pdf - secure document file. Open with Adobe Reader
.pps - slideshow presentation. Open with PowerPoint
.ppt - presentation file. Open with PowerPoint
.sys - system file.
.txt - text file. Open with Notepad
.wav - audio file. Open with Windows Media Player
.xls - spreadsheet file. Open with Excel
.zip - compressed file. Open with WinZip
