Or use the simpler built-in method that looks for the file in the same sxs folder:

Windows will download the required files automatically.

They run side-by-side. Installing .NET 3.5 will not break modern applications. Windows intelligently routes older apps to the 3.5 runtime and newer apps to 4.x or Core.

You need this file if:

to download the ISO that matches your current Windows version and architecture (e.g., x64). Mount the ISO : Right-click the downloaded ISO file and select Locate the File : Navigate to the \sources\sxs folder on the mounted drive. Find the Package : Look for the file named microsoft-windows-netfx3-ondemand-package.cab