Option 1: Install Offline Using Windows 10 Media (Recommended)

To install .NET Framework 3.5 on Windows 10 64-bit without an internet connection, you can use the tool or the Windows installation media. Since .NET 3.5 is a built-in "Feature on Demand," it is already included on your Windows 10 installation disk or ISO file. Method 1: Using Windows Installation Media (Recommended)

DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:X:\sources\sxs