Checkbox changes a downloadable PDF button to active state

Hey there - anyone know how to create a checkbox that the USER clicks to ‘activate’ a downloadable PDF button?

It’s for a prospectus download - legally you must agree to terms first. Seems pretty basic but I can’t think how to do it.

Similar to this site: The button becomes ‘active’ changes colour and is clickable - only AFTER the user ticks the checkbox???


THANK YOU SO MUCH from Sunny Perth Western Australia!