How To Open An Unknown File In Windows

How To Open An Unknown File In WindowsHow To Open An Unknown File In Windows

Whilst downloading items off of the internet, you can often come across files that are unknown to you and the computer. The file’s icon appears blank, you have no awareness of what the file is or how to open it, and the Windows operating system has no clue either on how to open it.

This is the issue we are going to be addressing today in this post; how do you open an unknown file type?

Understanding How Windows Knows Which App to Use

Have you ever wondered how the Windows operating system knows just which app or program to use when opening up a file? For example, if you open a “.doc” or a “.docx” file, chances are that it is going to open the file in Microsoft Word.

Each app or program has associated file types, or file extensions, that lets Windows know that the program is capable of handling such files. File extensions help your Windows OS recognize which file types are related to which applications, so that the appropriate one may be used to run the file.

File extensions are defined by the few letters in the file’s name after the period “.”

Learn how to show or hide file extensions.

That is how it is determined which app or program will the file open in.

If you are wondering how this information is relevant to opening an unknown file, then you are right on the queue. A file becomes “unknown” to the computer because of two main reasons:

  • There is no file extension defined.
  • There is no app or program installed on the PC to handle that type of file.

There are workarounds for both these problems and methods to get that file open in no time.

Open an Unknown File Type

There are a few ways you can go about the process to open an unknown file on a Windows computer. However, before doing any of those, it would be beneficial if you can find the file extension.

Follow the methods below in the given chronological order to attempt to open an unknown file.

Find the File Extension

The first thing you ought to do is find the file extension of the unknown file. As previously mentioned, this would be a 3 or 4-letter code at the end of the file name separated by a period.

You may find the file extension in the name of the file itself, provided that you have enabled showing file extensions.

File extension in name
File extension in the name

If you do not find the file extension here, you can look for it in the file’s properties. Here is how:

  1. Right-click the unknown file and click Properties.

    Open file properties
    Open file properties
  2. Look for the file extension in front of “Type of file“.

    Determine file type from properties
    Determine file type from properties

When you know the file extension, you can use this information to download a tool or an app from the internet that can handle/open those kinds of files.

In the case you do not find a file type, you must define one.

Assign a File Extension

In case the unknown file has no type defined, it is up to you to define it so the appropriate application can be used to open it.

Before you define a file type, you must know exactly what file it is. For example, if you know that it is a simple text file, you can set its file type to “.txt” and it should be opened with Notepad (or any text editor). However, if it is an image file and you set its extension to “.txt,” the image will not open and you will see scrambled characters in a Notepad.

Therefore, you must know the file type beforehand. For example, if you know that someone emailed you a video but with a missing file extension, defining its file extension as “.mov” or “.mp4” will be appropriate.

Here is a detailed guide to changing a file type.

Select an App to Open Unknown File

Sometimes, an application that can handle a file type is available on the computer, but the file just does not pick it up. In such a scenario, you must manually select the app to open the file with.

  1. Right-click the unknown file and click “Open with” from the context menu.

    Open with
    Open with
  2. Now, from the Open with dialog, select an app to open the file with.

    If you do not find the app here, click “Choose an app on your PC” and then browse for the app and select it.

    Alternatively, you can also download an app from Microsoft Store by clicking “Browse apps in the Microsoft Store,” where the Store app automatically picks up the file extension and suggests apps that can open it.

    Select an app to open the unknown file with
    Select an app to open the unknown file with

The file should then open in the selected app, provided that you have chosen the correct one.

Use Third-Party Apps

There are certain online services as well as applications that can be used to open unknown files. They automatically detect the type of file and open it for you.

You can use the following online service to upload and open an unknown file:

FILExt Online File Viewer

FILExt online unknown file analyzer
FILExt online unknown file analyzer

Alternatively, you can also use the following software to install it on your Windows PC and open all types of files with it. This tool also detects and opens many different file types.

File Magic – Universal File Viewer

File Magic Universal File Viewer
File Magic Universal File Viewer


It can be said that most, if not all, unknown files can be opened on a Windows PC using a few tools and tricks. This article guides you on how to find a file extension and then use it to find an appropriate app to open the file We have also given insight on tools that can be used to open a file even if its file extension is unknown.

With that said, we advise caution while opening an unknown file, as it may harm your computer if it contains malware.

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Subhan Zafar is an established IT professional with interests in Windows and Server infrastructure testing and research, and is currently working with Itechtics as a research consultant. He has studied Electrical Engineering and is also certified by Huawei (HCNA & HCNP Routing and Switching).

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