There are times while you are surfing the Internet when you may click on a file to download and your system may respond with an error message.  If the error message reads"Unknown file type, please choose an application to view files of this type", then you may be unable to view that file.  Different file formats require different viewers or plugins in order for you to see them correctly.  It is very common for your web browser to not understand all formats when it is first installed.  When you encounter files you cannot open, make not of the extension in the name of the file.  A file name will usually have the format "filename.xxx" where xxx (the part following the period) is called the extension.  Once you know the extension, it is usually quite easy to find and download a plugin that will allow your system to view these files.  Often, links to free viewers are contained on the web page where you loaded the file from.

The following is list of some common extensions, along with a short description, and information on how to view or where to get viewers.

You can also refer to this site for any file extension types not listed below.

 

Extension	Format Description & Type	Plugin/Application Required
.avi	Audio/Video Interleave. A popular video format	Windows Media Player
.doc	Microsoft Word Document	Microsoft Word
.exe	Program/executable	Double-click an .exe to launch the application or setup program
.gif	Graphical Interchange Format. A common image format found on the Internet	Image editing/viewing software will display .gif files. Windows comes with MS Paint
.htm/.html	HyperText Markup Language. Web page text is formatted using HTML	Displaying .html requires a web browser. Microsoft Internet Explorer and Netscape Communicator are both popular browsers.
.jpg/.jpeg	Joint Photographic Experts Group. A common image format used to display photographs and other high color images	Image editing/viewing software will display .gif files. Windows comes with MS Paint
.midi	Musical Instrument Digital Interface. A popular sound format on the Internet	Windows Media Player
.mov	A popular video file type	Requires Apple QuickTime, available at www .apple.com
.mp3	Mpeg Layer 3 Compression. Alternate audio type that creates files much smaller than .wav audio files. The average file size of an MP3 is about 1MB per minute of music.	Numerous MP3 players are available. Winamp, available at;www.winamp.com, is the most popular.
.mpg/.mpeg	Movie Producers Expert Group. The most common video format on the Internet	Two popular mpeg players are Windows Media Player and Real Player. Real Player is available at; www.realaudio.com
.pdf	Adobe's Portable Document Format. .pdf files are viewed using Adobe's Acrobat Reader	Adobe's Acrobat Reader is freeware . It is available at; www.adobe.com
.rar	WinRAR - A compression utility similar to Winzip	WinRAR is available at; www.rarsoft.com
.wav	A common sound format found on the Internet	Windows Media Player
.xls	Microsoft Excel spreadsheet	Microsoft's Excel
.zip	The most common file compression format.	Winzip is shareware and is available at; www.winzip.com