What Extension?

Have you ever wondered what all the different file extensions mean? How about trying to figure out what extension to use? You may not even know that you are using one type that will work with one program but not another.File extensions are the three letters that come after the dot in a file name. For example, a setup program might be called something like setup.exe. The ".exe" is the file extension and are used to let the computer know what type of file it is dealing with. For example, if the file is a ".jpg" file, the computer knows it is an image file. It is not recommended to change the extension.

Here’s a list of common extensions with descriptions and comments or cautions. Some of the ideas above from "MalekTIps: File Extensions Help and Tips."

Also, go to "Software Tips & Tricks: File Extensions" to see a complete alphabetical list of extensions, more than you ever believed existed.





an executable, or program file. This contains code that the computer follows in order to perform a particular task

Do not double click on this file if you receive by Email. Only Windows can open .exe files


a plain-text file that can be viewed with any word processor or notepad

Open Word or the word processing program first and then open the .txt file


Portable Document Format created by Adobe Systems’ (Adobe Reader- http://adobe.com) or shareware/freeware

Allows people to read, comment, fill out forms on a document without using a specific program. Adobe offers a for-pay online site, “Create Adobe PDF Online” (http//createpdf.adobe.com) to create PDF files, offering a five document free trial.


a document file that can contain text, images, photos, or any other type of information commonly found in word processing documents.

Some .doc files can contain viruses so only open files you know are from someone you know and trust


represents a Microsoft PowerPoint presentation, or slide show. StarOffice (http://www.sun.com/software/star/staroffice/index.xml), can also read and modify these files. .pps is a PowerPoint show only and can be read without opening the program.

Windows: PowerPoint Viewer 2003 Macintosh: PowerPoint 98 Viewer can view .ppt files. Some .ppt files contain macros that can harm your computer. Only open files from people you know and trust.


Rich Text Format file is a text file and any .doc or .ppt outline can be saved as .rtf

makes the text file readable in almost any word processor


Excel spreadsheet

can be exported as .xls or .csv for comma separated text files


Graphic Interchange Format for images

use this type with small image files, clipart, or animated gifs to be read by most browsers

.jpg or .jpeg

Joint Photographic Experts Group for images

use this for photos that you want to compress for the Internet


a QuickTime multimedia file.

QuickTime player is free but you can purchase a more robust program from Apple.


WAV (WAVE) files are audio files playable via multimedia playback software such as Windows Media Player (http://malektips.com/windows_media_player_help_and_tips.html)

WAV files normally take up a lot of room on hard drives and are being used less nowadays, especially for full songs.


Motion Picture Experts Group is an audio file

standard format for music that can compress the sound data into a small file


Flash files

animated or motion files that need a plug in to run

.ins or .isf

Inspiration or Kidspiration files that you can use for visual learning and graphic organizers. Trial versions can be downloaded from Inspiration (www.inspiration.com)

suggest saving as .gif for the diagrams or .rtf for outlines so others who may not have the program can open them


identifies an HTML page that contains Server Side Include, or SSI, directives to include another file, show date last modified, etc.

using this extension helps keep the server from slowing down - without this extension the server has to parse files looking for SSI directives.

Submitted by: Barbara Bray

Next Tip: Hiding and Finding Extensions