Identify my dotnet version

Use Environment.Version - it gives you the exact version of .NET running the application.

Gets a Version object that describes the major, minor, build, and revision numbers of the common language runtime.

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To find out what version of the framework is installed, see this SO question and answers. In a nut shell, you will need to dig into the registry.

You can use the:

Environment.Version

to get the version number of the .NET runtime.