Sometimes it´s good to check if the desired version of the Microsoft .NET Framework is installed on the target machine where you want to run your code, ah, app. Fortunately, this is easy to figure out.
See MSDN article How to: Determine Which .NET Framework Versions Are Installed for .NET versions and How to determine which versions and service pack levels of the Microsoft .NET Framework are installed.
To check the version open a command prompt, and start
regedit. In the Registry Editor locate the Registry Key "
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP" and check the value for the related .NET Framework.
The value of the Release DWORD indicates which version of the .NET Framework is installed (copied from here - you can also check with code.)
Value of the Release DWORD
378389 - .NET Framework 4.5
378675 - .NET Framework 4.5.1 installed with Windows 8.1
378758 - .NET Framework 4.5.1 installed on Windows 8, Windows 7 SP1, or Windows Vista SP2
379893 - .NET Framework 4.5.2
For FW minor 4 see here for the values for each version.
To check the CLR Version open Visual Studio Command Prompt and run the CLR Version Tool
BTW: If you´re interested in Benefits of the Microsoft .NET Framework check that website.
See also this post Overview about the Microsoft .NET Versions.