File Extensions

File Associations and Related File Types


1. What is a file extension?

A file extension is the suffix after the dot at the end of a filename. For example, in the filename "document1.txt", the file extension is ".txt". This suffix is used to identify the file type and helps your computer choose an appropriate program to open the file.

While the majority of file extensions use three characters, some have less while others have more. For example, ".ai" and ".pages". Many new file types now use longer extensions.

For more information about file extensions, view the complete file extension definition.

2. What is a file type?

A file type is a name given to a specific type of file. For example, the plain text file type commonly uses the ".txt" extension. The Photoshop document file type uses the ".psd" extension. The file type is the first information listed on each file extension page.

3. What is a file association?

A file association is a relationship between a file type and an application that can open the file. When you double-click a file, your computer uses the file association to determine what program will open it. Both Windows and Macintosh systems allow you to change file associations by opening a file's properties and selecting another application to open the file.

4. Can I change a file extension?

It is possible to change a file extension, but it is usually not recommended. When you change a file's extension, you also change the file association. If the extension does not match the file type, your computer may be unable to open the file.

5. Can I submit a file extension to

Sure, I am continually adding new file extensions on a regular basis. Just submit your extension to the administrator. Be sure to include the file type, a detailed description of the file, and what applications can be used to open the file.

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