how to install .net framework 3.5 offline version on windows 10 or windows 8 pc. .Net framework has been an important missing installation from newly installed windows 8 and windows 10. However, it is something wish has been placed and hidden a bit in the Windows installation folder. Our main objective is to pull that out. How to install .net framework 3.5 offline version for windows 8/10 Method 1 First, make sure you have a Windows installation disk or image. As I am pretty much sure you do have before you run the installation Now, mount the image and give it a drive letter. You don't need a third-party software in Windows 10 before doing this. Just right click on the image file and select mount.