Windows 10 (64-bit) includes .NET Framework 3.5 as an optional "Windows Feature." It is not installed by default to save system resources, but the installation files are built into the operating system image to facilitate easy activation without requiring an external download.
For the average Windows 10 64-bit user, . Instead, enable .NET Framework 3.5 directly from Windows Features . If you need a fully offline installation, use the DISM command with a Windows 10 installation ISO. download .net framework 3.5 windows 10 64 bit
If the above method doesn't work (which is rare), or you prefer a direct download: Windows 10 (64-bit) includes