Did you just run into a file that has been digitally signed by .NET? If that's the case, please read on.
You will typically notice .NET when double-clicking to run the file. The publisher name shows up as the "Verified publisher" in the UAC dialog as the screenshot shows:

You can view the digital signature details for .NET with the following steps:
Here's a screenshot of a file that has been signed by .NET:

As you can see in the screenshot above, Windows reports that "This digital signature is OK". This means that the file has been published by .NET and that no one has tampered with the file.
If you click the View Certificate button shown in the screengrab above, you can view all the details of the certificate, such as when it was issued, who issued the certificate, how long it is valid, and so on. You can also view the address for .NET, such as the street name, city and country.
Microsoft Code Signing PCA 2011 has issued the .NET certificates. You can also see the details of the issuer by clicking the View Certificate button shown in the screenshot above.
The following are the .NET files I have gathered, thanks to the FreeFixer users.
| Detection Ratio | File Name |
|---|---|
| 0/69 | System.Text.Json.dll |
| 0/68 | WindowsFormsIntegration.resources.dll |
| 0/70 | System.Xaml.resources.dll |
| 0/71 | System.Runtime.CompilerServices.Unsafe.dll |
The detection percentage is based on that I have gathered 278 scan reports for the .NET files. 0 of these scan reports came up with some sort of detection. You can review the full details of the scan reports by examining the files listed above.
The analysis has been done on certificates with the following serial numbers: