Complete Reference Guide📖 What is a File Extension?
A file extension (also called a filename extension or file suffix) is a set of characters added to the end of a filename after a period (dot). It typically consists of 3-4 letters and serves as an identifier for the file type.
Example Filename:
document.pdf
| Filename: | document |
| Extension: | .pdf |
| File Type: | PDF Document |
Purpose of File Extensions
🎯 Identification
Tells users and applications what type of data the file contains (text, image, video, etc.)
🔗 Association
Links files to default programs. Double-clicking a .pdf opens your PDF reader automatically.
🔒 Security
Helps identify potentially dangerous files (.exe, .bat) that could harm your system.
document.pdf.exe might appear as document.pdf. We recommend enabling file extension visibility in your system settings.⚙️ How File Extensions Work
File extensions are part of a broader system that helps computers manage files. Here's how the process works:
1. File Creation
When software saves a file, it adds the appropriate extension based on the format chosen (Save as PDF → .pdf)
2. MIME Type Mapping
Extensions map to MIME types (e.g., .pdf → application/pdf) which define how data should be handled
3. OS Recognition
Operating systems maintain a registry of extensions and their associated programs
4. Program Launch
Double-clicking opens the file with the registered default application for that extension
Extension vs Format vs MIME Type
| Concept | Definition | Example |
|---|---|---|
| File Extension | Visible suffix in filename | .jpg, .pdf, .docx |
| File Format | Internal structure/encoding of data | JPEG, PDF, Office Open XML |
| MIME Type | Internet standard identifier | image/jpeg, application/pdf |
photo.jpg to photo.png doesn't convert it to PNG format - it just confuses the operating system. Use proper conversion software for format changes.📚 File Extension Categories
File extensions are organized into categories based on their purpose and the type of data they contain. Click any category to explore all extensions within it.
📄 Document Files
Document files contain formatted text, tables, images, and other content for reading, editing, and sharing information.
🖼️ Image Files
Image files store visual information including photographs, graphics, icons, and artwork.
🎵 Audio Files
Audio files contain sound recordings, music, voice, and other audio content.
🎬 Video Files
Video files contain moving images, often with audio.
📦 Archive Files
Archive files combine multiple files into one and often compress them to save space.
🗄️ Data Files
Data files store structured information used by applications for configuration, databases, and data exchange.
📧 Email Files
Email files store electronic messages, mailboxes, contacts, and calendar information.
🌐 Web Files
Web files are used to create and deliver content on the internet.
⚡ Programming Files
.IPYNB⚡ Executable Files
Executable files contain programs that can run on your computer. Handle with caution.
🔤 Font Files
Font files contain typeface data used to display text in specific styles.
📚 eBook Files
eBook files contain digital publications including books, magazines, and comics.
📐 CAD & 3D Files
CAD and 3D files store technical drawings, 3D models, and design specifications.
💿 Disk Image Files
Disk image files contain exact copies of storage media content.
🔧 System Files
System files are used by operating systems for configuration, drivers, and core functionality.
🎮 Game Files
Game files include saves, ROMs, mods, and game-specific data formats.
🔤 Alphabetical Index
Browse all file extensions alphabetically.
N
.NEF❓ Frequently Asked Questions
A file extension is a suffix at the end of a filename, typically 3-4 characters after a period (e.g., .txt, .jpg, .pdf). It tells the operating system and users what type of file it is and which program should be used to open it.
Windows 10: Open File Explorer → Click the "View" tab → Check "File name extensions"
Windows 11: Open File Explorer → Click "View" → "Show" → "File name extensions"
Yes, you can rename a file to change its extension. However, this does NOT convert the file to a different format. The file's internal structure remains the same. To properly convert files, use conversion software.
File Extension: The visible suffix in the filename (e.g., .jpg, .pdf, .docx).
File Format: The actual internal structure and encoding specification (e.g., JPEG, PDF, Office Open XML).
Common reasons: No compatible program installed, corrupted file, wrong file extension, or the file requires specialized software. Try identifying the correct file type and installing appropriate software.
Windows: Not case-sensitive (.JPG = .jpg)
Linux/Unix: Case-sensitive (.JPG ≠ .jpg)
macOS: Usually not case-sensitive
For cross-platform compatibility, use lowercase extensions.
MIME (Multipurpose Internet Mail Extensions) type is an internet standard identifier for file formats. Examples: text/html for HTML, image/jpeg for JPEG, application/pdf for PDFs.
📝 Summary: Understanding File Extensions
- File extensions identify file types and associated programs
- They appear after the period in filenames (e.g., .pdf, .jpg)
- Changing the extension doesn't convert the file format
- Extensions map to MIME types for internet use
- Over 500+ extensions exist across 16+ categories
- Common categories: documents, images, audio, video, archives
- Be cautious with executable files (.exe, .bat, .sh)
- Keep extensions visible for security awareness
