I just wanted to experience Windows 8.1 as I spent too much time on Windows 10, that's why I downgraded it. I just got Windows 10 back yesterday after posting the first post. Anyway I downloaded this NET Framework, and when I double click on it, it doesn't show up. I checked the task manager, no changes.
One more point which's, I already tried the NET Framework 4.7, but it told me it's already installed on my device, but I checked the Programs and Features in Control Panel, I couldn't find any NET Framework version.