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File Extensions

Did you ever get an attachment to an email and when you clicked on it, the computer asked YOU what program should be used to open it! And you thought the computer was all-knowing!

When this happens, the computer has looked at the "type" of file and was unsuccessful in finding just the right piece of software to open that file. This is where "file extensions" come into play. File extensions are like the DNA of the computer in that they tell the computer what program was used to create a file. Conversely, the extension also tells the software program, such as Microsoft® Word, that the file and the program speak the same language.

File extensions are automatically added to each file created and saved on a computer. As example, say you just created a letter to Aunt Bell using Word and saved this file as "Aunt Bell." Word will automatically include a file extension of .doc or the new .docx. The file name will become Aunt Bell.doc. Knowing a number of the commonly used file extensions will help you open those pesky files that contain Aunt Bell's secret recipes.

Category/Program	Extension	Extension Description
Word Processing
Microsoft Word Microsoft Works Microsoft Works WordPerfect	.doc .wks .wps .wkb, .wp, .wp4, .wp5, .wp6	Word Document Works Document Works Text Document WordPerfect Document
Universal Formats	.txt .rtf .csv	Text Rich Text Format Comma-separated value text file
Spreadsheets
Microsoft Excel Microsoft Excel Lotus QuattroPro	.xls .xlw .wks, .wk1, .wk3, .wk4 .wb1, .wb2,.wb3	Excel Spreadsheet Excel Workbook Lotus spreadsheet various versions QuattroPro Notebook, Spreadsheet, Text file
Database
Microsoft Access Microsoft Visual FoxPro & dBase	.mdb .dbf	Access Database FoxPro & dBase Database
Graphic
Microsoft Picture It! Apple QuickTime Adobe PhotoShop Corel Draw Corel Photo Paint Adobe Acrobat Reader Paint	.mix .mov .psd .cdr .cpt .pdf .bmp	Picture It! Picture File QuickTime Movie PhotoShop Bitmap Corel Draw Vector Drawing Corel Photo-Paint image Adobe Portable Document Format Standard bit-mapped graphics format
Generic Picture Formats	.bmp .eps .jpg .gif .tif	Standard bit-mapped graphics format Encapsulated Postscript image file JPEG-Joint Photographic Experts Group Graphics Interchange Format Tagged Image File Format
Audio (Music)
Windows Media Player, RealPlayer, Media Jukebox	.mp2,.mp3 .wav .mid .aif	MPEG Audio File(music) Waveform audio file Standard MIDI file (music synthesizers) Audio Interchange File
Business Presentation
Microsoft PowerPoint	.ppt	PowerPoint Presentation
Web Browsers
Microsoft Internet Explorer, Netscape, Mosaic, Lynx	.html .xml	Hypertext Markup Language eXtensible markup language

Software programs can open a variety of file types such as Microsoft Word will open a standard Word document (.doc), Web pages (.html, .htm), Rich Text Format (.rtf), Text files (.txt), Microsoft Excel (.xls and .xlw), etc. One of the most common file types found on the Web is the Adobe Portable Document Format (.pdf). Many forms will be saved in the PDF format and can be read using the free Adobe Acrobat Reader. (Download at http://www.adobe.com/products/acrobat/readstep2.html).

For an extensive listing of file types go to http://www.file-extensions.org/.