If you are a developer working in Visual Studio and need to build an application that specifically targets .NET Framework 4 (not 4.5, 4.6, or 4.8), you will need the . This pack allows your IDE to reference the correct assemblies, show the correct API documentation, and ensure your application runs on systems with only .NET Framework 4 installed.
If you are checking the file system, the reference assemblies are typically installed to: C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0
