To permanently remove the watermark of ‘Activate Windows 10’, you need to enter the genuine product key. So if you have upgraded your system to Windows 10, you need to enter a valid product key. Even if you are not facing any issues while using the updated operating system, still to remove the watermark, this is one of the options. You can also try running Windows Activation troubleshooter to get rid of the annoying watermark of Windows 10. Also, if you don’t have a product key, you can get a new one from Microsoft.