Type the following command and press : dism /online /enable-feature /featurename:NetFx3 /All
Press . You will see a progress bar (0.0% to 100%). This takes 2–5 minutes.
Or simply check Control Panel > Programs > Turn Windows features on or off – .NET 3.5 should be checked.
After restarting, you can verify that .NET Framework 3.5 is successfully installed.
Or use the built-in source option:
While Windows includes this framework, it is often disabled by default to save space and resources. When you try to run an older app, Windows might prompt you to download the required files, which sometimes results in errors (such as Error Code 0x800F081F). In these scenarios, manually downloading and installing the Microsoft-windows-netfx3-ondemand-package.cab file is the most reliable workaround.