To install .NET Framework 3.5 on Windows 10 64-bit, users should attempt to download the framework from third-party websites. The most reliable method is enabling it via the "Turn Windows features on or off" menu. If internet access is restricted, the DISM command-line tool using Windows 10 installation media provides a robust offline installation alternative.
If you have the Windows 10 installation media (ISO) mounted as drive D: : download .net framework 3.5 windows 10 64 bit