Common File Extensions

For reference, a list of common file extensions you may encounter on your PC or in the web.

Extensions for Text Document Files

.txt: files containing plain text, which doesn't contain formatting (bold, italics, paragraphs, font size, etc.). These can be opened by Notepad or Notepad++.

.pdf: a PDF document, which shows "pages" like in real life with text and images on them. It can be opened by an application called a PDF reader. This format is often used for printing.

.html: an HTML document. It can be opened by any web browser. This is, literally, a webpage as a file.

Note: Microsoft Office formats are listed further below.

Extensions for Image Files

.bmp: bitmap image format. An uncompressed image format used by Windows.

.png: PNG image format. An compressed, lossless image format.

.jpg, .jpeg: JPEG image format. A compressed, lossy image format.

.gif: GIF image format. An uncompressed image format that supports animated images, but has a color palette limited to 256 colors.

.webp: a modern image format for the web. Not supported by some old software. Can be lossy or lossless, supports transparency, and can be animated.

.svg: a SVG (Scalable Vector Graphics) image. These can typically be viewed in your web browser. To edit them you would need a SVG editor like Inkscape.

.ico: an icon file. Although this is a proprietary Windows format, it's de facto the standard format for favicons. This requires an image editor with specialized support to create because a single .ico file can contain multiple versions of the same icon at different resolutions.

.cur: a cursor icon file. This also requires specialized support to edit because a cursor file has a special attribute indicating the "hotspot" of the cursor, which is the position of the pixel on the icon that would be at the tip of the arrow cursor, or the equivalent on other cursor states.

.raw: an image format used by digital cameras and scanners.

.tiff: another image format used in photography.

Extensions Used by Image Editors

Each image editor typically has its own proprietary file format to save project files [Why Every Image Editor has its Own Image Format?]. Some examples:

.psd: a Photoshop file. This should be opened in Photoshop, although other applications may (partially) support opening this file.

.kra: a Krita file.

.xfc: a GIMP file.

Extensions for Video Files

Note: the file extension os a video file indicates the format of the video container. A video container contains one or more video streams, audio streams, and even other data like subtitles. For each of these, an appropriate codec is necessary in order to encode the stream while saving the video and decode the stream while opening the video. This means even if an application supports one format, it may have issues opening it if it doesn't have the necessary codecs to load the streams within.

.mp4: MPEG-4 container format. This can be opened in most video players and video editors.

.gifv: a MP4 file that is supposed to be displayed like a GIF (without audio, looping automatically). This was invented by Imgur, a website where people upload GIFs, and is also used by Tumblr.

.webm: a WebM file. This is a video format created for the web. It's not widely supported.

.avi: a widely supported video format.

.wmv: a Windows video format.

Extensions for Zipped Folders & Compressed Archives

.zip: a zipped folder. This isn't a normal folder which contains multiple files inside. To the system, it's a single file. Some programs can open it to see what's inside, but many programs can't, so it has to be "unzipped" into a normal folder first.

.rar: a WinRAR archive (or RAR file). WinRAR is a proprietary application that can compress files into its own format of zipped folder. They let you unzip RAR files for free. Many have never bought WinRAR.

.7z: extension used by 7zip, which is another software for creating zipped folders.

.tar.gz: a Tarball archive that has been compressed with the GNU's Gzip compression algorithm. This is typically used in Linux, specially to package source code.

Extensions Used in Windows

Windows Programs

.exe: an executable file. Double clicking on such file runs the program stored inside the file.

.dll: a DLL (Dynamic-Link Library). Complex programs typically use subprograms that come from other projects created by other programmers. Although it's possible to merge the subprogram into a single .exe, there are cases where that isn't a good idea for one reason or another, e.g. it can be illegal if the license doesn't allow it, such as the GPL license. This means the programmer must ship the third party subprograms as separate files, and DLLs are the format of such files on Windows. For example, libpng.dll is a library that can process PNG image files. Program that can process PNGs typically come with this library.

.msi: an executable file that is an installer.

Extensions used by Office Applications

Microsoft Office Extensions

Note: old MS Office file formats were binary files, new formats are based on XML and their extensions end in x.

.doc, .docx: a rich text file used by Microsoft Word.

.xls, .xlsx: a spreadsheet file used by Microsoft Excel.

.ppt, .pptx: a presentation file used by Microsoft PowerPoint.

Extensions for Portable Data

.csv: a CSV (Comma Separated Values) file. This is a plain text file that describes a table or spreadsheet. Typically, in a program that can display a table, you will be able to "export as CSV" in order to import it in a spreadsheet softwared such as Microsoft Excel or LibreOffice Calc.

.rtf: "Rich Text Format." This is a proprietary Windows format created to be portable in the 90's.

.xml: an XML (eXtensible Markup Language) file. This is a plain text file containing XML code. The data itself can be anything, but being in XML format means that there are countless tools you can use to process and edit these files.

LibreOffice Extensions

.odt: text document by LibreOffice Writer.

.ods: spreadsheet file used by LibreOffice Calc.

.odp: a presentation file used by LibreOffice Impress.

Extensions used by Websites

.html: the HTML source code for a webpage.

.css: the CSS source code for a webpage.

.js: the Javascript source code.

.min.css, .min.js: minified source code. These files are generated by using a minifier program like Uglify to make source code files smaller.

.rss: an RSS feed.

.atom: an RSS feed that is in ATOM format.