To support applications requiring the .NET Framework 3.5 on Windows 10 clients, the framework must be added manually.
The Windows 10 Add/Remove Features snap in will allow you to manually add the .NET 3.5 Framework to your system, but it requires a connection to Windows Update. If your clients aren’t able to connect to Windows Update (for example if they are behind a proxy, or some other firewall rule that denies access) then you’ll need to specify an alternate source for the installation files.
To add the .NET Framework 3.5 features to a Windows 10 client via an alternate source, use the following command in an elevated PowerShell session.
Add-WindowsCapability –Online -Name NetFx3~~~~ –Source D:\sources\sxs
Please remember to change the Source path to the location of your source files.