DOC Microsoft Word is the word processor program included with Microsoft Office. If you just need to view or print the document, we recommend using the Word Viewer. If you need to edit or modify the document, you will need to use OpenOffice
DOCX DOCX Word Documents are different than the DOC version in that they use the Microsoft Office Open XML format. The Open XML format makes it easy for other programs, such as OpenOffice.org, to read DOCX files (and other Open XML file types). The Open XML format was introduced with Microsoft Office 2007.
DOCM File created by Microsoft Word, a program used for word processing; contains embedded macros that can be executed within the document; used to automate Word Open XML document (.DOCX) tasks by adding advanced macro functionality.
DOCM files are saved using the open XML-based Word document format, which was introduced in Office 2007. They can be opened by Microsoft Word 2007 or previous versions of Word with Open XML component support.
RTF Common text file format that supports "rich text;" may include several types of text formatting, such as bold type, italics, different fonts and font sizes, custom tab settings, etc; may also support images saved within the text file.
TXT 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.
Generic text files with filenames that ending in ".txt" are created by Notepad for Windows and by TextEdit for Mac OS X when document formatting is removed.
Various hardware devices, such as smartphones and the Amazon Kindle also recognize plain text files.
PPT Microsoft PowerPoint is a presentation tool included with Microsoft Office. PowerPoint allows you to make interactive multimedia slideshows to present information. When you open a PowerPoint Presentation (.ppt, .pptx), the PowerPoint software is launched, but the presentation doesn't start automatically. If you want the presentation to start immediately in full screen mode and provide a more polished and professional experience, you should save it as a PowerPoint Show. 
PPTX Presentation file created by Microsoft PowerPoint, a program used to create slide show presentations; contains a collection of slides, including their text, images, formatting, animations, drawn objects, and other media; commonly used in business meetings, marketing applications, and academic classroom settings.
In contrast to .PPT files, which store all presentation data in a single binary file, PPTX files are created using the Open XML format, which stores documents as a collection of separate files in a compressed zip package. The file types include XML document properties, images, macros, charts, and other media files.
File types in PPTX files are also more accessible than those in PPT files. For example, slide notes are accessible as plain text files and slide images are stored as separate image files within the PPTX file.
PPTX files can be opened by PowerPoint 2007 or later for Windows, or with PowerPoint 2008 or later for Mac OS X. They are also backwards compatible with previous versions of PowerPoint for Mac and Windows via Open XML component support.
XLS Microsoft Excel is the spreadsheet software included with Microsoft Office. Excel spreadsheets created with Office 2007 or newer use the file extension .XLSX instead of .XLS. If you just need to view or print an existing spreadsheet you can use the Excel Viewer. If you need to edit or create a new Excel spreadsheet you will need to use OpenOffice.org.
XLSX Microsoft Excel is the spreadsheet software included with Microsoft Office. Excel spreadsheets created with Office 2007 or newer use the file extension .XLSX instead of .XLS. If you just need to view or print an existing spreadsheet you can use the Excel Viewer. If you need to edit or create a new Excel spreadsheet you will need to use OpenOffice.org.
XLSX Excel Spreadsheets are different than the XLS version in that they use the Microsoft Office Open XML format. The Open XML format makes it easy for other programs, such as OpenOffice.org, to read XLSX files (and other Open XML file types). The Open XML format was introduced with Microsoft Office 2007. 
ODT Text document created with Writer, the Apache OpenOffice and StarOffice word processor; formatted using the OASIS OpenDocument XML-based standard.
OpenDocument text files can be opened and edited with any OpenOffice-compatible program, including: NeoOffice (Mac), AbiWord (Mac & Windows), and KWord (Unix). They can also be imported into Google Docs, Google's Web-based word processor and spreadsheet application.
HTML Hypertext Markup Language, or HTML, is the primary programming language used by website developers to display content. Your web browser, such as Internet Explorer or Firefox interprets the HTML code and displays the result.
MHTML Web page archive format saved from a .HTML file and encoded with .MIME encoding; includes resources linked from the Web page, such as images, Flash animations, Java applets, audio files, etc; can be opened and viewed without being online.
PDF  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; can be edited with Adobe Acrobat, a commercial program.
PDF files can be opened and viewed using the free Adobe Reader or the Adobe Reader plug-in, which is available for most Web browsers. Google, Bing, and other search engines now index PDF documents, so the Adobe Reader plug-in is commonly used when viewing search engine results. Some browsers, such as Google Chrome, provide native support for PDF viewing without the Adobe Reader plug-in. Also, Firefox can view PDF files with the PDF.js extension.
PDF files may contain text, images, forms, annotations, outlines, and other data. They preserve fonts and formatting electronically across multiple platforms and appear the same on the screen as they will when printed on paper.
JPG Compressed image format standardized by the Joint Photographic Experts Group (JPEG); commonly used for storing digital photos since the format supports up to 24-bit color; therefore, most digital cameras save images as JPG files by default.
JPEG is also a common format for publishing Web graphics since the JPEG compression algorithm significantly reduces the file size of images. However, the lossy compression used by JPEG may noticeably reduce the image quality if high amounts of compression are used.
TIF High-quality graphics format often used for storing images with many colors, such as digital photos; short for "TIFF;" includes support for layers and multiple pages.
TIFF files can be saved in an uncompressed (lossless) format or may incorporate .JPEG (lossy) compression. They may also use LZW lossless compression, which reduces the TIFF file size, but does not reduce the quality of the image
TIFF High-quality graphics format often used for storing images with many colors, such as digital photos; short for "TIFF;" includes support for layers and multiple pages.
TIFF files can be saved in an uncompressed (lossless) format or may incorporate .JPEG (lossy) compression. They may also use LZW lossless compression, which reduces the TIFF file size, but does not reduce the quality of the image
EMF Windows vector graphics format recognized by many image-editing applications; basically a 32-bit version of the original Windows Metafile Format (.WMF), which only supports 16-bit data; saves image data in an RGB format and does not support CMYK data.
WMF Proprietary Windows graphic format developed by Microsoft; contains a series of drawing operations, including commands for drawing lines, circles, and rectangles; may also contain bitmap drawing operations; used primarily for vector images, but can also include raster graphics.
WMF files originally appeared in 1988 with the release of Windows 2.0. Microsoft later published the WMF file format specification with the Windows 3.1 release in 1992, and then published a subsequent specification in 2006.
WMF files have largely been replaced by more standard formats, such as .JPG and .GIF images. The WMF format is still supported by various programs, including Microsoft's Windows Photo Viewer, which is included in Windows 7.
BMP Uncompressed raster image comprised of a rectangular grid of pixels; contains a file header (bitmap identifier, file size, width, height, color options, and bitmap data starting point) and bitmap pixels, each with a different color.
BMP files may contain different levels of color depths per pixel, depending on the number of bits per pixel specified in the file header. They may also be stored using a grayscale color scheme.
GIF Image file that may contain up to 256 indexed colors; color palette may be a predefined set of colors or may be adapted to the colors in the image; lossless format, meaning the clarity of the image is not compromised with GIF compression.
GIFs are common format for Web graphics, especially small images and images that contain text, such as navigation buttons. However, JPEG (.JPG) images are better for showing photos because they are not limited in the number of colors they can display.
GIF images can also be animated and saved as "animated GIFs," which are often used to display basic animations on websites. They may also include transparent pixels, which allow them to blend with different color backgrounds. However, pixels in a GIF image must be either fully transparent or fully opaque, so the transparency cannot be faded like a .PNG image.
PNG Image file stored in the Portable Network Graphic (PNG) format; contains a bitmap of indexed colors and uses lossless compression, similar to a .GIF file but without copyright limitations; commonly used to store graphics for Web images.
The PNG format was created in response to limitations with the GIF format, primarily to increase color support and to provide an image format without a patent license. Additionally, while GIF images only support fully opaque or fully transparent pixels, PNG images may include an 8-bit transparency channel, which allows the image colors to fade from opaque to transparent.
PNG images cannot be animated like GIF images. However, the related .MNG format can be animated. PNG images do not provide CMYK color support because they are not intended for use with professional graphics. PNG images are now supported by most Web browsers.
TGA Raster graphic file format designed by Truevision; supports 8, 16, 24, or 32 bits per pixel at a maximum of 24 bits for RGB colors and and 8-bit alpha channel; often used to store texture files referenced by 3D video games.
The Targa format, which stands for Truevision Advanced Raster Graphics Adapter, was designed by Truevision (now Pinnacle Systems) in 1984 for use with its first video software programs
PCX Raster image format developed by ZSoft; became one of the original bitmap image formats for the DOS/Windows platform; supports 24-bit color images, 8-bit grayscale and indexed color images, and 1-bit black and white images; compressed using RLE encoding.
The PCX file format has mostly been replaced by newer image formats, but is still used by some fax and scanning applications. Multi-page PCX fax documents use the .DCX extension.