Air Canada Travel Voucher Transfer Questions

Hello, with all the Air Canada Travel Vouchers that are being given out I'm starting to see them come up for sale and am thinking about buying one off someone to save some $$.

I have questions about how the transfer works though. So they give you the voucher code and pin and then you get access to the voucher, I would assume they still have access to it at this point if they have the same info? Then how do you transfer it to your account/make it so you are the only person who can access it? Air Canada's website just mentions that its fully transferable but doesn't say much else.

Just looking to cover my bases if I do it to ensure its a more secure transaction, does anyone have experience with this?

Thanks