Protecting your Thank You/Download pages from direct visits… by newbies, at least!
This one comes up periodically in the Community, so thought I'd set out the answers for next time.
Thank You (a.k.a. Follow Up/Download) pages shown after a lead converts are public webpages, just like the Landing Pages that host your forms. So occasionally the concern flares up that people will post or forward the Thank You URL, encouraging other leads to bypass the form and go straight to the Download button.