Install W10 Pro without having a key yet ?

Install W10 Pro without having a key yet ?

I am helping a friend with his Asus laptop. The hard drive is damaged, and there is no hope of using the recovery (re-install) partition on his hard drive.
He was wary of the cost of a new drive, and the cost of a new W10 Pro license, and is seriously considering purchase of a new laptop.
I have popped in a second hand 40GB drive, that scans OK, and I would like to do the following -
1) Download the W10 64bit ISO (I am doing that now, using the Media Creation Tool running in my W10 desktop)
2) Install the W10 64bit ISO into his laptop/
3)Demonstrate it to him, and tell him that all he has to do is purchase a license within 30 days.

Is all of that do'able ?
IE Can I install it now and register it a bit later ?

Thanks,
Rob
PS I have an unused copy of W8 Pro (still in the box with a License)
I offered to give that to him, but his wife(who owns the laptop) is convinced that Software being released now and in the future, won't work in W8. I don't believe that is the case. What do you all think ?

PPS I was responding guys, when the later posts came in, so I am a bit confused.
I will hold back from muddying the waters until I read the links in the latest post

HippsieGypsie said:

He can use any legitimate 7, 8 or 10 key of the same edition as long as it's not installed on another machine. It should also self activate with digital license tied to his MS account if he has one.

Yeah - just skip key entry during installation - it will activate automatically.

Plankton said:

Since this is a laptop....odds are that it's an OEM install and most likely wont self activate using the ISO from the media creation tool. More than likely a phone call to MS to reactivate it is going to be needed. And for that you can use this link.......
Activate Office 2010 - Office Support

I do not think you really know what you are talking about.

Firstly link is for MS Office not Windows.

Secondly, virtually all installations get granted a digital licence unless running a very old version of Windows 10.

It is totally irrelevant if it's an oem install or a retail stand-alone install.

Anyway, as hard drive has failed, and unless he had a record of original key, how could MS reactivate it anyway?

Even if key was oem, OP would not need to call MS.

OP would only need to call MS if there was no digital licence, and the oem key (assuming he knew it) failed to activate. This is VERY UNLIKELY.

HippsieGypsie said:

OEM or not it will activate. Here's some reading and help on the subject.

New motherboard Processor - Windows 10 Forums

Activate Windows 10 Installation Upgrade Tutorials

Use Activation Troubleshooter in Windows 10 Installation Upgrade Tutorials

Reading original post again, it is ambiguous - OP needs to clarify if Window 10 was already being run on PC prior to disk failure. If it was, it will activate almost certainly.