File Extension Reference

Understanding File Extensions

A file extension is the suffix at the end of a filename (after the dot) that indicates the file format. For example, in "document.pdf", the extension ".pdf" tells the operating system and applications that this is a PDF document.

File extensions are important because they:

• Help your operating system determine which application should open a file
• Indicate what type of content a file contains
• Provide a first indication of whether a file might be safe to open

Browse the categories below to find information about specific file types, or use the alphabetical listing at the bottom of this page.