Have you ever downloaded and tried to open a file… only to find that it doesn’t work? Or you expect the content to open in one program, but your computer tries to use a completely different one?
Or the worst scenario: you click on a file, and your computer asks, “Which program?” You don’t know! You thought the computer would know for you!
Files are built of several different interconnected parts, and if your file isn’t opening as expected, you likely have a file extension problem.
File extensions are the short suffixes at the end of file names. Some of the most common you’ve likely seen include:
• .pdf
• .jpg
• .docx
• .mp3
These short labels are small, but are integral to how the file is used by your device. Knowing what they are (and what they should be) can help you know why your files may or may not be working.
It can also help you protect yourself from clicking on malicious links or downloading dangerous files that can damage your device and compromise your security.
What Is A File Extension?
A file extension is the end of a file name, typically in the format of “filename.extension”. The type of extension tells you the type of file you’re working with, but more importantly, it tells your computer or other device what to “do” with the file when it’s activated.
When you double-click a file, your device’s operating system goes to work, checking the extension and deciding what to do next. For instance, a .pdf file will be opened by your default PDF viewer. A .mp3 is opened in your music app.
The extension also determines what icon you’ll see and how your device interprets the data in the file itself. Think of it as a package with a label. The file is the package, and the file extension is a label that says “this is a document!” or “this is a photo!”
Does Changing a File Extension Mess Up the File?
Here’s a common situation that makes sense in theory, but often messes up the process. Imagine you have a PowerPoint slideshow that you present in a meeting. Your manager then asks for you to send them the presentation in a PDF file.
So you rename the file from slides.pptx (a PowerPoint extension) to slides.pdf (the PDF file extension). But when your manager tries to open the file, nothing happens. The problem is that you’ve changed the name of the file, but not the data inside the file itself. A PDF viewer will try to open the slides.pdf file, but can’t do anything with it.
But this doesn’t mean the file is messed up or broken! In most cases, you just need to revert the file back to its original name and extension, and then use the program to export the presentation as a PDF file.
When It’s OK to Change an Extension (and How to Do It Safely)
There may be times when you need to change a file’s extension. And in some cases, you can change the extension in the name of a file as long as the file type is similar.
For example, you can change a file name such as photo.jpg (a compressed photo file) to photo.png (a photo file type that has data transparency) and still open the image safely.
However, if you tried to change photo.jpg into a document file (photo.docx), the file won’t open properly. The image is still there, but your device can’t do anything with it.
When you need to change a file, you can check the software or program that opens the file and use the “export” or “Save As” feature to change the file. But take note: sometimes you simply can’t change the file type because of what the file is.
A Note About Viruses, Phishing, and Other Security Risks
One reason to know how file extensions work is the security aspect. Every day, individuals download viruses or give hackers access to their devices by clicking on nefarious files.
A common file extension risk is the “double extension”. For example, you may receive an email with an attached file titled invoice.pdf.exe, a file that may look like a PDF file, but is actually an executable file that runs a program when clicked.
Always be extra cautious when receiving files from unexpected emails. If you didn’t expect to receive the file or if something seems out of place, assume it’s dangerous to open. Antivirus software can also help you stay protected from dangerous files.
The Most Common File Extensions
Here are some of the most common file extensions and what they are used for:
Documents
| Extension | What It Is | Opens With |
|---|---|---|
| Portable Document Format | Adobe Acrobat, web browsers | |
| .docx | Microsoft Word document | Word, Google Docs, LibreOffice |
| .pptx | PowerPoint presentation | PowerPoint, Google Slides, Keynote |
Images
| Extension | What It Is | Opens With |
|---|---|---|
| .jpg | Compressed photo format | Photos app, browsers, Photoshop |
| .png | Image with transparency | Photos app, browsers, Photoshop |
| .gif | Animated or static image | Web browsers, image viewers |
Videos
| Extension | What It Is | Opens With |
|---|---|---|
| .mp4 | Standard video format | VLC, QuickTime, browsers |
| .mov | Apple QuickTime video | QuickTime, VLC, iMovie |
| .avi | Older Windows video | VLC, Windows Media Player |
Audio
| Extension | What It Is | Opens With |
|---|---|---|
| .mp3 | Compressed audio file | Spotify, iTunes, VLC |
| .wav | Uncompressed audio | VLC, Audacity, media players |
| .m4a | Apple audio format | iTunes, Apple Music, VLC |
Why Knowing About File Extensions Matters
It may seem simple, but knowing what file extensions are and how they work can help you use digital content more effectively. It can also help you avoid clicking on dangerous or broken files.
You don’t need to memorize the entire list of file extensions. Instead, get to know the main extensions in specific file types, such as documents, videos, audio, and photos. You’ll appreciate how much easier it is to use, send, and download files once you know exactly what you’re working with!
