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File Extensions. Those Letters at the End of Your Files Explained.
       

So, you received an attachment from a colleague containing THE important information you need for your big production. But wait! It won’t open! What kind of file is it anyway? Making note of the file extension at the end of the file name can help you find the correct program needed to open it. Below you can find some common file extensions and what they mean. READ THE COMPLETE ARTICLE HERE.

Common File Extensions:

Microsoft Word	Adobe Acrobat	Corel Word Perfect	Microsoft Excel
Some extensions relate to the software that was used to create or read them. Others are general and cross-platform.

.doc – Microsoft Word Document. Created by Microsoft Word, the most popular word processing program; included with all versions of Microsoft Office; may contain formatted text, images, tables, graphs, charts, page formatting, and print settings.
.pdf – Portable Document Format File. Cross-platform document created by Adobe Acrobat or a program with the Acrobat plug-in; commonly used for e-mail attachments or for saving publications in a standard format for viewing on multiple computers; usually created from another document instead of from scratch. To download the Acrobat Plug-in go to: http://get.adobe.com/reader/otherversions/
.txt – Plain Text File. Standard text document that contains unformatted text; recognized by any text editing or word processing program; can also be processed by most other software programs.
.wpd – WordPerfect Document. Text document created by Corel WordPerfect, a popular word processing application; supports formatted text, tables, forms, and images; saved in a proprietary Corel format, but can be exported to other formats from within WordPerfect.
.xls – Microsoft Excel Spreadsheet. Spreadsheet created by Microsoft Excel, the most widely-used spreadsheet program; stores data in a table with rows and columns; table cells can contain manually entered data or the results computed from the data of other cells; can also be used to create charts and graphs.
.exe – Windows Executable File. DOS or Windows executable program or self-extracting archive; runs when opened; any Windows file that ends in ".exe" should run when double-clicked. "SETUP.EXE" and "INSTALL.EXE" are common installer files included with Windows software. EXE files will not run in Mac OS X, but can be run using emulation software, such as Parallels Desktop for Mac.

Compressed Files:

When sending large files over email it is often useful to compress them into smaller files that can be uploaded and downloaded faster, and then be un-compressed later. Some common compressed files are as follows:

WinZip		StuffIt
Compression software adds its own extension, but when un-compressed, the files retain their original extensions.

.zip – Zipped File. File compressed or "zipped" using Zip compression, a common type of compression in which every file in the archive is compressed separately; supported by most file compression/decompression programs. Windows users can create ZIP files using a program such as PKZip or WinZip; Mac OS X users can create ZIP archives by right-clicking a file and selecting "Create Archive of [filename]." To un-zip a file try: http://www.winzip.com/index.htm for Windows or http://my.smithmicro.com/mac/stuffit/index.html for Macintosh.
.sit - Stuffit Archive File. Compressed file "stuffed" by Smith Micro StuffIt software; common file compression format used on Macintosh systems; originally Mac-only, now cross-platform, meaning SIT files can be created and opened on both Macintosh and Windows platforms. Download it at: http://my.smithmicro.com/mac/stuffit/index.html

Multi-Media:

Internet boundaries are ever-expanding and web developers are waist deep in multi-media projects that they are trying to deliver to as many people as possible all over the world. Therefore, developers have created all kinds of graphic, video and audio formats that boast the highest quality without forcing their audience to sit through the download process all day. Before we decipher these formats, it is important to know some basics about compression.


Common Graphic File Extensions:

.jpg / .jpeg – JPEG Image File. 
Named after the Joint Photographic Experts Group, JPEG is a lossy codec for storing and transferring full-color digital images that's often used to post photography and artwork on the Web. JPEG compression takes advantage of the human eye's inability to see minute color changes, removing portions of data from the original picture file. When creating a JPEG file, varying amounts of compression can be selected, depending on the desired file size and image quality.

File size: 11k	File size: 8k	File size: 7k
The above .jpg files show the result when compressing graphics to acheive smaller file sizes. Notice the quality loss. A compression software, such as one shown above, can temporarily shrink the file size for sending via email, and be un-compressed later, retaining their original size and quality.

.gif - Graphic Interchange Format. 
A format for storing digital images, commonly used for bullets, icons, and other graphics on the Web. The GIF format is limited to 256 colors, so it's not as commonly used as JPEG for storing digital photos. A single GIF file can combine several frames together for basic animated motion.
.tif - TIFF Image File Format. 
TIFF is a flexible container format for digital still images, commonly used in desktop publishing. TIFF images can incorporate various forms of compression (like JPEG), or can be uncompressed. Some digital cameras offer a special TIFF mode for capturing uncompressed photos; however, these files require many times more storage space than JPEGs, and can quickly fill up your camera's available memory.

Adobe Illustrator		Adobe Photoshop
Some extensions relate to the software that was used to create them, and can ONLY be opened by those programs.

.ai – Adobe Illustrator File. Vector image file created by Adobe Illustrator; composed of paths, or lines connected by points, instead of bitmap data; may include objects, color, and text; often referred to as an Illustrator drawing.
.psd – Photoshop Document. Document created by Adobe Photoshop, the most commonly used professional image editing program; can include image layers, adjustment layers, layer masks, annotation notes, file information, keywords, and other Photoshop-specific elements.

Video File Extensions:

Windows Media Player	Quicktime		Flash
There are a variety of file types with a variety of quality and compatibility options. Here are some examples.

.qt / .mov - 
QuickTime Movie. A file format for storing and playing back movies with sound. Though developed and supported primarily by Apple, Inc., this flexible format isn't limited to Macintosh operating systems — it's also commonly used in Windows systems and other types of computing platforms. In Windows, QuickTime files usually appear with the ".MOV" filename extension. DOWNLOAD QUICKTIME PLAYER FOR FREE AT: http://www.apple.com/quicktime/download/
.wmv - Windows Media Video. 
Microsoft's proprietary lossy compression format for motion video. Windows Media Video is used for both streaming and downloading content via the Internet. Microsoft's Windows Media Player, an application bundled with Windows Vista operating systems, lets you play back and manage a range of audio and video file types, including WMA and WMV. DOWNLOAD WINDOWS MEDIA PLAYER: http://www.microsoft.com/windows/windowsmedia/player/10/default.aspx
.avi - Audio/Video Interleaved. 
A file format for storing and playing back movie clips with sound on Windows-based PCs. An AVI file is organized into alternating ("interleaved") chunks of audio and video data. AVI is a container format, meaning that it specifies how the data will be organized, but is not itself a form of audio or video compression.
AVI is the type of file that's created when DV clips are imported from a digital camcorder to a PC. (These clips are often referred to as "DV-AVIs" because they contain full-quality digital video content.)
MPEG. 
MPEG stands for Moving Picture Experts Group — a committee that sets international standards for the digital encoding of movies and sound. There are several audio/video formats which bear this group's name. In addition to their popularity on the Internet, several MPEG formats are used with different kinds of A/V gear:
.mp1 - This format is often used in digital cameras and camcorders to capture small, easily transferable video clips. It's also the compression format used to create Video CDs, and commonly used for posting clips on the Internet. The well-known MP3 audio format (see definition below) is part of the MPEG1 codec.
.mp2 - Commercially produced DVD movies, home-recorded DVD discs, and most digital satellite TV broadcasts employ MPEG2 video compression to deliver their high-quality picture. MPEG2 is also the form of lossy compression used by TiVo-based hard disk video recorders. It can rival the DV format when it comes to picture quality. Because MPEG2 is a "heavier" form of compression that removes a larger portion of the original video signal than DV, however, it's more difficult to edit with precision. The MPEG2 codec allows for selectable amounts of compression to be applied, which is how home DVD recorders and hard disk video recorders can offer a range of recording speeds. MPEG2 is considered a container format.
.mp4 / .m4v - A flexible MPEG container format used for both streaming and downloadable Web content. It's the video format employed by a growing number of camcorders and cameras.
.swf / .flv – Macromedia Flash Movie. Animation created by Adobe Flash (formerly Macromedia Flash); can include text as well as both vector and raster graphics; plays in Web browsers that have the Flash plug-in installed; most Web browsers come with a recent version of the Flash plug-in.

Audio File Extensions:

.mp3 - MPEG1, Audio Layer 3. 
The most popular codec for storing and transferring music. Though it employs a lossy compression system which removes frequencies judged to be essentially inaudible, MP3 still manages to deliver near-CD sound quality in a file that's only about a tenth or twelfth the size of a corresponding uncompressed WAV file. When creating an MP3 file, you can select varying amounts of compression depending on the desired file size and sound quality.
.wav 
- WAVE Audio File. A standard audio format for Windows operating systems, often used for storing high-quality, uncompressed sound. WAV files can contain CD-quality (44.1 KHz/16-bit) audio signals. However, CD-quality WAV files require relatively large amounts of memory — roughly 10 MB per minute of music. WAV is a container format.
.wma - Windows Media Audio. 
Developed by Microsoft, Windows Media Audio is one of today's most pervasive Internet audio formats. Though not as popular as MP3, proponents of lossy WMA claim that it can outperform MP3 in the area of sound quality, particularly with files encoded at lower bitrates such as 64 or 96 Kbps. This performance advantage makes it handy for applications like portable digital audio players, where total play time is limited by a finite amount of internal memory.
The Windows Media Audio format features built-in copy protection abilities, unlike MP3. Windows Vista, Microsoft's current flagship operating system software, contains native support for WMA encoding, enabling users to create their own WMA music files. Don’t have Windows Media Player? DOWNLOAD IT NOW AT: http://www.microsoft.com/windows/windowsmedia/player/10/default.aspx

For more information about file extensions go to: http://www.fileinfo.com/common.php where you can find a comprehensive searchable database of all file extensions and their associated programs.