Thank you for clarifying..
I am assuming you already have the program loaded, Office 2016?
If so, let me correct a misunderstanding you have. Starting with office 2013 but mainly with 2016, Microsoft does not use keys exlusively anymore.
Instead, they use usernames and passwords, as keys can be faked, or otherwise stolen or altered.
So, what we need to focus on is what is the email address for the microsoft account that you need in order to reinstall office 2016 down the road.
So if you have office installed, you should be able to open word or another office program and click
It should show the email address / account that your office ( key ) is tied to.
Then, to reinstll office down the road, you go to this page http://www.office.com/myaccount
Sign in using your office accounts registered email address and password.
And then click to download or install office.
So what you need here is in reality, to know the email address that your office is registered to, as long as you have that then you can always sign in down the road should you need to download office again.
If you get stuck, or have any further questions, let me know.