Is it an actual buyer (someone who has actually bought something from you) or a potential buyer who has not made a purchase.
In the first case it is permissible to ask for their email address and send the PDF as an attachment to the email.
"Laissez-faire capitalism (AKA The Great Material Continuum) is the only social system based on the recognition of individual rights and, therefore, the only system that bans force from social relationships." ~ Ayn Rand
