Windows 10: Windows 8.1 Pro upgrade key good for Windows 10

I just bought a brand new Dell Ryzen 2700X desktop computer that came with Windows 10 Home. It came with version 1709 from the factory. I tried several different product keys I have for Windows 10 Pro to do the upgrade to Pro and all of them I had were rejected. I have a Windows 8.1 Home to Pro upgrade product key (retail), the computer for which it was used is long gone. Thought I would try it. And it worked! Found it very interesting. Now that I have a digital license for Pro for my new computer, I'm going to restore an image I made of my old desktop computer so I can easily keep all my programs, apps, and settings. It is Windows 10 Pro as well.

:)

 

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Now that I have finally upgraded from Windows 8 to Windows 10 will my Windows 8 key work with a fresh install of Windows 10?

 

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I read through most of that thread and it seems you have to jump through windows insider hoops. Is there a Retail Windows 10 x64 PRO ISO I can download directly from microsoft that my windows 8 key will work with?

 

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Thanks but I don't want to do any decrypting. I want to download a Win 10 ISO from Microsoft and install it using my Win 8 key. No other steps required. Is that possible?