If for whatever reason you need to install .Net Framework 3.5 on a Windows 10 device that is not connected to the internet you can by installing it from the original Windows 10 image using Powershell or Command Prompt.
If for whatever reason you need to install .Net Framework 3.5 on a Windows 10 device that is not connected to the internet you can by installing it from the original Windows 10 image using Powershell or Command Prompt.