Have you ever wondered what those letters after the dot in a file name mean? For example, in the file name `document.docx`, what does `docx` stand for? And why does it matter? In this blog post, we will answer these questions and more. We will explain what a file extension is, how to change the program associated with a file extension, how malware writers use extensions to trick you into running a virus, and some common file extensions you should know. Let's get started!
What are file extensions?
A file extension is a suffix that indicates the type and format of a file. It usually consists of two to four letters or numbers, and is separated from the file name by a dot. For example, in the file name `image.jpg`, the file extension is `jpg`, which stands for JPEG, a common format for digital images.
A file extension tells the computer and the user what kind of file it is, and what program can open it. For example, a file with the extension `pdf` can be opened by a program that can read PDF files, such as Adobe Acrobat Reader. A file with the extension `mp3` can be played by a program that can play MP3 audio files, such as Windows Media Player.
A file extension also helps the user to identify the file by its icon. For example, a file with the extension `docx` will have an icon that looks like a document with the letter W on it, indicating that it is a Microsoft Word document. A file with the extension `xlsx` will have an icon that looks like a spreadsheet with the letter X on it, indicating that it is a Microsoft Excel workbook.
How to change the program associated with a file extension
Sometimes, you may want to open a file with a different program than the one that is associated with its file extension by default. For example, you may want to open a PDF file with Google Chrome instead of Adobe Acrobat Reader. Or, you may want to open a JPG file with Photoshop instead of Windows Photo Viewer.
To change the program associated with a file extension, you can follow these steps:
- Right-click on the file you want to open, and select `Open with` from the menu.
- If the program you want to use is listed, select it. If not, select `Choose another app`.
- A window will pop up with a list of programs that can open the file. Select the program you want to use, and check the box that says `Always use this app to open .xxx files`, where `xxx` is the file extension. Then, click `OK`.
- The file will open with the program you selected, and the icon of the file will change accordingly. From now on, whenever you double-click on a file with that extension, it will open with the same program.
How malware writers use extensions to trick you into running a virus
Unfortunately, not all files are what they seem. Some malicious files may have a fake or hidden file extension, designed to trick you into running a virus or malware on your computer. For example, a file may have a name like `invoice.pdf.exe`, but only show `invoice.pdf` as the file name. If you double-click on it, thinking it is a PDF file, you may end up running an executable file that can harm your computer.
To avoid falling for this trick, you should always check the full file name and extension before opening a file, especially if it comes from an unknown or suspicious source. You can do this by enabling the option to show file extensions in Windows Explorer. To do this, you can follow these steps:
- Open Windows Explorer, and click on the `View` tab.
- In the `Show/hide` section, check the box that says `File name extensions`.
- Now, you will be able to see the full file name and extension of every file in Windows Explorer. If you see a file with a double extension, such as `invoice.pdf.exe`, or an extension that does not match the file type, such as `image.txt`, be careful and do not open it.
Common file extensions
There are thousands of file extensions in use, but some are more common than others. Here are some of the most common file extensions you should know, and what they stand for:
- `.docx`, `.doc`: Microsoft Word document
- `.xlsx`, `.xls`: Microsoft Excel spreadsheet
- `.pptx`, `.ppt`: Microsoft PowerPoint presentation
- `.pdf`: Portable Document Format, a document file that can be viewed on any device
- `.jpg`, `.jpeg`: Joint Photographic Experts Group, a compressed image file format
- `.png`: Portable Network Graphics, an uncompressed image file format that supports transparency
- `.gif`: Graphics Interchange Format, an image file format that supports animation
- `.mp3`: MPEG-1 Audio Layer 3, a compressed audio file format
- `.mp4`: MPEG-4 Part 14, a compressed video file format
- `.zip`: Zip, a compressed file format that can contain multiple files or folders
- `.exe`: Executable, a file that can run a program or a software
- `.html`, `.htm`: HyperText Markup Language, a file that contains the code for a web
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