This is what I need:
"Email Before Download" presents your users with a form where they submit information, like their name and email address, prior to receiving a download. This plugin allows you to create any form you like and manage/monitor your file downloads. You can also EXPORT a list of users that have downloaded files from the plug-in's settings page.
To be clear - I don't want to make a client put this into a shopping cart and checkout. This is for a free whitepaper offer only.
Wordpress has one, why not Shopify?
https://wordpress.org/plugins/email-before-download/