I recently experienced an issue on my professional Windows 10 laptop.

It was impossible for me to add the “.NET Framework 3.5 (includes .NET 2.0 and 3.0)” feature.

This is required by some applications or games, even if you have the latest .NET framework installed on your machine (4.7 for example).

I had the following error while doing so:

Windows Features Windows couldn’t complete the requested changes. Windows couldn’t find required files to complete the requested changes. Make sure you’ re connected to Internet, and try again. Error code: Dx8DOFD81F

I found the reason and the fix from this page:
https://support.microsoft.com/en-us/help/2734782/net-framework-3-5-installation-error-0x800f0906-0x800f081f-0x800f0907

The laptop was already installed when I got it and I guess some items have been removed from Winsxs (or the update group policy is jammed), the goal here is to install this feature from Windows 10 installation ISO.

Here is how to fix this:

1. You need to know which version of Windows 10 you’re running.
   Details can be found here: https://www.howtogeek.com/236195/how-to-find-out-which-build-and-version-of-windows-10-you-have/
2. Download from http://my.visualstudio.com/ your Windows 10 version ISO file (if you don’t already have it) and mount the ISO (right click > mount)
3. Run the following command from a DOS window with admin rights: (replace D with the drive letter)
   Dism /online /enable-feature /featurename:NetFx3 /All /Source:D:\sources\sxs /LimitAccess

You should see something nice like this: