Have you ever clicked on a file and your computer said, “Windows can’t open this file”? That means you’re looking at an unknown file type — something your system doesn’t recognize. Don’t worry! You don’t need to be a tech expert to fix this. In this complete guide, we’ll explain what unknown files are, why they show up, and the best ways to open unknown files safely on your Windows PC, Mac, Android, or iPhone.
What Is an Unknown File?
An unknown file is any file that your computer, phone, or tablet can’t identify because it doesn’t know which program should open it. Every file type usually ends with a file extension — like .jpg, .pdf, .mp3, or .docx. These extensions tell your operating system what kind of file it is and which software to use to open it.
For example:
- A file ending in .jpg opens in a photo viewer.
- .mp3 opens in a music player.
- .pdf opens in Adobe Reader.
But if your file doesn’t have an extension, or if the extension isn’t linked to any program, your computer calls it “Unknown file” or “Unknown format.”
Sometimes this happens because the file got renamed, corrupted, or downloaded from the internet without proper formatting.
Why Files Show as Unknown
There are several reasons a file shows up as an unknown format or unrecognized. Let’s break them down:
- Missing File Extension:
- The most common reason is that the file extension got removed. Without .txt, .mp4, or similar endings, your computer doesn’t know what to do with the file.
- Wrong File Association:
- Maybe the extension is correct, but your computer doesn’t have an app linked to open it. For example, .heic files (from iPhones) might not open on older Windows systems.
- Corrupted File:
- Sometimes, a file gets damaged during download, copying, or transferring from another device, making it unreadable.
- New or Rare File Format:
- New apps or software can create unique file types that older systems don’t recognize — like .sav, .blend, or .crdownload.
- Malware or Fake Files:
- Some “unknown” files might actually be unsafe. Malicious programs often hide under weird extensions to trick users into opening them.
Understanding the reason helps you decide the right way to open or repair unknown files safely.
How to Open an Unknown File?
If your computer says it can’t open a file, don’t panic. You have several easy ways to figure it out and fix it. Below are step-by-step tips anyone can try.
Check the File Extension
First, look at the file name. If it ends with something like .abc, .xyz, or nothing at all, you need to check its extension.
Windows:
- Right-click the file and select Properties.
- Look for “File type.”
Mac:
- Right-click → Get Info.
- Look for “Kind.”
If the file has no extension, you can rename it and add one — for example, change unknownfile to unknownfile.pdf or unknownfile.jpg.
Then try opening it again.
You can also Google the extension. For instance, searching “.sav file open” can tell you which program supports that format.
Use Online File Identifier Tools
There are smart tools online that analyze your file and tell you what it really is. They check the file signature (metadata) inside, not just the extension.
Here are some of the best online file identifier tools:
- TrIDNet (Windows) – Detects over 13,000 file types.
- CheckFileType.com – Quick and free.
- OnlineTrID – Upload your file and get instant identification.
- Filext.com – Helps match unknown extensions with software.
Simply upload your unknown file, and the tool will show what type it is and which apps can open it. This works even if the file extension is missing or fake.
Try Opening with Common Programs
Sometimes, a file might just be mislabeled. Try opening it in one of these universal programs:
- Notepad (Windows) or TextEdit (Mac) – For small files that might be plain text.
- VLC Media Player – Can open most video and audio formats.
- WinRAR or 7-Zip – Try if the file could be compressed (like .zip, .rar, .tar).
- Microsoft Word or Google Docs – For text or document-based unknown files.
- Photoshop or Paint.NET – For image files.
- Hex Editor Neo – Shows raw file data, useful for advanced users.
If one of these programs can read even a small portion of the file, you’ll know what type it is.
How to Identify a File Type Without Opening It
You can often identify a file without opening it using your operating system’s built-in tools or third-party apps.
On Windows:
- Right-click → Properties → “Type of file.”
- Use Command Prompt → assoc command to see associations.
- Install TrID or FileAlyzer for deep inspection.
On Mac:
- Use Terminal → file command (e.g., file filename).
- It tells you the file’s format based on internal data.
Online Tools:
Websites like GetInfo.io, File-Extensions.org, and WhatIsThisFile.com can identify files using metadata even if you don’t open them.
What to Do If the File Still Won’t Open
If your unknown file still doesn’t open after identifying it, you may need to convert or repair it.
Try a File Converter
- CloudConvert, Zamzar, or Convertio can change almost any file format to another supported one.
- Example: convert .heic → .jpg, or .pages → .pdf.
Re-download or Restore File
If the file came from an email, website, or USB stick, it may have been corrupted. Try downloading it again.
Check for Software Updates
Sometimes, your software is just outdated. For instance, older versions of Microsoft Office can’t open new .docx files until updated.
Ask the Sender
If someone sent you the file, ask which program they used to create it. That can solve the mystery instantly.
Tools That Help Open Unknown Files
When manual steps fail, specialized tools can help you open, view, or convert unknown files.
Best Free File Viewers
- Free File Viewer Lite – Opens 200+ formats, including text, images, media, and archives.
- Universal Viewer – Lightweight and supports multimedia and documents.
- File Viewer Plus – Paid version adds editing and converting.
- Quick View Plus – Great for businesses handling mixed files.
- Multi Commander – Combines file management and viewing tools.
These programs let you preview unknown files without risk.
File Type Converters
Converters change files from one type to another so your computer can recognize them.
Popular options:
- Zamzar.com – Simple drag-and-drop conversion.
- CloudConvert.com – Handles 200+ file types.
- FreeConvert.com – Works for audio, video, images, and documents.
Always choose trusted converter tools to avoid malware or data leaks.
Antivirus Scanners
Before opening any unknown file, scan it for viruses or malware.
Good antivirus programs include:
- Windows Defender (Free)
- Malwarebytes
- Bitdefender
- Avast
- Norton 360
These tools detect and remove hidden threats that often disguise themselves as unknown files.
Stay Safe While Opening Unknown Files
Opening unknown files can sometimes be risky. Always follow these safety steps:
- Never open unknown email attachments — especially .exe, .scr, or .bat files.
- Scan every file with an antivirus before opening.
- Avoid random file download sites.
- Keep your OS and apps updated.
- Use a sandbox tool like Windows Sandbox to test suspicious files safely.
By staying cautious, you protect your data, privacy, and devices.
The Bottom Line
Learning how to open unknown files isn’t complicated — it just takes patience and the right tools.
To summarize:
- Always check the file extension first.
- Use online file identifiers to detect format.
- Try opening with universal programs like VLC or Notepad.
- Use file converters for unsupported formats.
- Always scan for viruses before opening.
By following these simple steps, you can safely open, convert, and use any unknown file — without worrying about damaging your system or losing data.
