Going from Windows 8.1 to Windows 7?

I picked up a laptop from someone and it has Windows 8 on it. I had to do the factory reset option to clear the hard drive because apparently you can't use an OEM key with any of the W8 ISOs Windows provides on their website. I went through the reset, uninstalled a lot of the Asus bloatware, and upgraded it to Windows 8.1.

The thing is I'm not really ready for 8.1 yet, and I'd like to get Windows 7 on it. I got Acronis on it to image the hard drive so I will have an image of this clean 8.1 install for the future if I do decide to switch over. I heard there's all this stuff about UEFI boot that you need to disable in the BIOS and enable Legacy boot or something like that so you can boot from a DVD, but then the W8 key is stored in the BIOS or something so it makes it really hard even if you format the hard drive to do a clean install of Windows 7 and might even be impossible.

Can anyone give some insight to this? I tried to use this video to do it but his BIOS is configured differently from mine.

 

You have to enable legacy mode in BIOS. I also had to change the USB3 settings in BIOS because all of my USB ports are 3 and Windows 7 only natively supports USB2. It took me hours to find all the correct drivers even though HP has most of them listed. The only thing I'm having trouble with is that HDMI doesn't work. I just need to find the right drivers.

I have no idea about recovering the Windows 8 keys.