If you try to install using the "Turn Windows features on or off" menu without internet, you will see this. You must use the Command Prompt (DISM) method pointing directly to the .cab file you extracted from the ISO.
When you try to turn on .NET 3.5 via "Turn Windows features on or off" and it fails, it means your computer cannot download the files from Windows Update. Microsoft-windows-netfx3-ondemand-package.cab Download
dism /online /enable-feature /featurename:NetFx3 /all /source:D:\sources\sxs /limitaccess If you try to install using the "Turn
IT administrators often need to deploy the CAB to hundreds of offline machines. Microsoft-windows-netfx3-ondemand-package.cab Download
The safest and most legitimate way to "download" this package is to extract it directly from official Microsoft installation media.