File extension UNKNOWN doesn't belong to any particular application. Presense of these files usally indicates problems with Windows Registry or presense of malware.
Typical UNKNOWN application file locations:
Frequently associated Windows objects:
Open UNKNOWN File on Windows
Find a UNKNOWN file in question in Windows OS File Explorer and double click on it to launch the corresponding application.
If a UNKNOWN file is not opened in an application and you instead get a "Windows can't open a file" error message you should try looking for an application which can open the file in question.
If you know the application which can open UNKNOWN file then run it and see if there is a File->Open main menu option in the application.
If you don't know the application which function as UNKNOWN file opener then try to search online for "UNKNOWN viewer", "application to open UNKNOWN file" or "open UNKNOWN file" queries in the search engine you like.
Install the application you found and check if it can open UNKNOWN file
Open UNKNOWN File on Mac OS
Find a UNKNOWN file in question in Mac OS Finder and double click on it to launch the corresponding application.
If a UNKNOWN file is not opened in a Mac OS application and you instead get a "There is no application set to open the file" error message you can click on "Search App Store" in the error dialog and Mac OS will show you applications compatible with UNKNOWN file.
If you know the Mac OS application which can work as UNKNOWN file opener you can choose the "Choose Application..." option in the error box to associate the file extension and open UNKNOWN file in it.
If you don't know the application which can open UNKNOWN file then try to search for "UNKNOWN viewer", "application to open UNKNOWN file" or "read UNKNOWN file" queries in the online search engine you like.
Install the application you found and check if it can read UNKNOWN file
Open UNKNOWN File on Android
If you downloaded a UNKNOWN file on Android device you can open it by following steps below:
In the Android apps list on your Android device find "My Files" or "File manager" app and tap to start it.
Tap on "Downloads" folder inside the app.
You should see your downloaded UNKNOWN file in that folder.
Tap on the file. If Android device supports opening the file you downloaded it will open in the corresponding app.
If file does not open you can look for the corresponding app that can open the file by searching Android App Store for the "UNKNOWN".
If you cannot open the file with the apps from Android App Store it is possible that the file could only be opened on desktop platforms such as Windows or Mac OS. Try searching for "UNKNOWN viewer", "UNKNOWN file reader" online and see if any desktop applications can open it.
It is also possible that the file you downloaded is outdated and is no longer supported.
Open UNKNOWN File on iPhone or iPad
To open UNKNOWN File on iOS device follow steps below:
Open Files app on your iPhone or iPad device. You can find it by swiping down on the home screen and typing "Files" in the search bar.
Tap on the Downloads folder on the Files app home screen.
You will see all files that you recently downloaded. Tap on the UNKNOWN file to view it.
If you have the right app that can open it it will automatically launch and open your file.
If you don't have the app which can open it you need to serch Apple app store for "UNKNOWN". This way you can find apps which can open UNKNOWN files.
If this doesn't help it is possible that your file could be opened only by the desktop application. To find an app which can open it on desktop look for "UNKNOWN viewer" or "UNKNOWN file" online in your favorite search engine.
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