Additional checkout field to send download link only

I am currently setting up a b2b site where the retailer will be showing sales options to their customer who will pay them directly for a pdf download.

The retailer will purchase this via the site at a trade price, entering the customers email address in an extra field at the checkout.

The invoice receipt will send to the retailer and at the same time the download link will send direct to the customers email address entered preferably with the stores details but no pricing.

Is it possible to add this extra field and additional email?