How to send a document when someone clicks a button

I am wondering if there is a way for me to add a button to my site to "register" for a conference and then automatically send them a PDF email confirming registration.

Thanks for any help!

You would need a form (with at least an email field) rather than just a button, but this is very possible with email automations. You could use Squarespace email marketing or Mailchimp to set this up to send an email with a PDF after someone enters their email address.