This is the core "offline" method. We will use the Deployment Image Servicing and Management (DISM) tool to inject the framework files directly from the source.
On : Go to Control Panel > Programs > Programs and Features, then click on "Turn Windows features on or off." Check ".NET Framework 3.5 (includes .NET 2.0 and 3.0)" and follow the prompts. framework 3.5 offline