Acts as a managed execution environment (virtual machine) that provides various services to its running applications, including memory management and security.
If you meant you need a specific file, piece of code, or a fix related to .NET 4.0, please provide more details (e.g., error message, app name, or what you're trying to accomplish). software net framework 4.0
Here is an interesting, opinionated, and slightly unconventional guide to the .NET Framework 4.0. Acts as a managed execution environment (virtual machine)