This opt-in page is a good starting place for a landing page concept to opt-in for the doTERRA eBook for internal use series.
This page could be a hidden page within your site, and simply called by button, within an autoresponder, or even a conditional redirect within a form based on someones interest.
NOTE: Make sure to grab the associated form and autoresponder to get you started.
Form: doTERRA eBook - Internal
Autoresponder: doTERRA eBook - Internal