We’ve covered how to enable .NET 3.5.1 on Windows 8 developer preview since then there are so many changes in Release Preview and RTM version of Windows 8, even in RTM version it seems Microsoft doesn’t enabled .NET 3.5 by default and you’ll be prompted with Windows Features dialog to install .NET framework 3.5 when you try to run any app that requires .NET 3.5 on your Computer, let us see all three methods of installing .NET 3.5 on Windows 8:online, offline and through Win8 installation media.
Installing .NET 3.5 online
If you’ve got Windows Features dialog click on ”download and install this feature” (the above screenshot taken in RP dialog may be different in RTM which we don’t have access now) which connects to Windows Update site then downloads and installs necessary files on your computer.
Enable .NET 3.5 in Control Panel
Open Control Panel> Programs>Programs and Features > Turn Windows Features on or off select .NET framework 3.5 (includes .NET 2.0 and 3.0) and click Ok. Changes will be applied very quickly.
Adding .NET 3.5 via Win 8 installation media
Insert Windows 8 DVD in DVD drive and open command prompt with admin privileges and type the following command.
Dism /online /enable-feature /featurename:NetFx3 /All /Source:x:\sources\sxs /LimitAccess
I recommend you to follow the second method in Control Panel.