We've all been in this situation. We download a file from the internet, receive an email with an attachment, or find an old file on our computer, and when we try to open it, a message appears asking us what program we want to open it with. This happens because the operating system doesn't recognize the file extension, and therefore, doesn't know which program to use to open it.
🔍 Article Structure
🔵 Understanding file extensions
File extensions are a system that allows the operating system to associate file types with programs. There are thousands of extensions, but some are very common:
- .docx, .doc: Microsoft Word documents
- .xlsx, .xls: Excel spreadsheets
- . Pdf: PDF documents
- .jpg, .jpeg, .png, .gif: Pictures
- .mp3, .wav, .flac: Audio files
- .mp4, .avi, .mkv: Video
- .zip, .rar, .7z: Compressed files
In many operating systems, extensions may be hidden. You can show extensions through file explorer settings.
🔵 File type recognition
When you have a file with an unknown extension, try to determine its type:
- Check the extension in a database:
- Check the contents of the file:
- For text files: Open it with Notepad (Windows), TextEdit (macOS), etc.
- For binary files: Appears as unintelligible characters; requires specialized software.
- Use file type recognition tools:
- TRIDEM: Smart file type program
- fillet (Linux/macOS): Command line to check file type
- Exiftool: Reads file metadata
file αγνωστο_αρχειο.xyz
Many files have "file signatures", a place for specialized identification even without an extension.
🔵 Tools for opening unknown files
- File preview:
- Windows: Preview Pane
- MacOS: Quick Look (Space)
- Linux: File managers e.g. Nautilus
- Universal file viewers:
- Specialized programs:
- Binary processors (HxD, Hex Fiend, Bless)
- Media players (VLC, MediaInfo)
- Compression programs (7-Zip, WinRAR, The Unarchiver)
Some extensions (such as .xml) are opened with multiple programs.
🔵 Opening unknown files in Windows
- Right click > Open with: Select the application or set a permanent open for a file type.
- Default app settings: Settings > Apps > Default apps > Choose by file type.
🔵 Safe management of unknown files
- Before opening, scan with antivirus
- Use VirusTotal or virtual environment (VirtualBox, VMware)
- Avoid opening suspicious executables (.exe, .bat, .cmd)
- Even seemingly "innocent" files (e.g. .pdf, .docx) may contain dangerous macros or scripts
FAQ
1. Can I simply change the extension of a file to open it?
Not without knowing the actual type. Changing the extension does not convert the file; only if you correct an already incorrect extension!
2. What do I do if no program opens the file?
- Perhaps the file is corrupted or requires specialized software.
- Try data recovery/contact a specialist.
3. Is it safe to open files from unknown sources?
Never without checking with antivirus and not if you don't trust the source!
4. How do I see hidden extensions?
- Windows: Explorer > View > Options > View > uncheck "Hide extensions..."
- macOS: Finder > Preferences > Advanced > "Show all file extensions"
- Linux: Usually extensions are visible by default
🔵 Useful resources
- FileInfo.com - Extensions database
- File-Extensions.org - Thousands of extensions
- Super User - Questions and answers about computers
- Reddit r/techsupport - Technical support
- Exif Tool - Edit metadata
- VirusTotal - Online file check
🔚 Conclusion
Managing unknown files becomes easy if you know the steps. Identify type/extension, choose appropriate program, check for viruses, be careful with executables! Use specialized tools and consult the above resources for any questions!
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