I imagine you would be able to use one of the email marketing tools to set up email automation (ie. when someone completed a transaction, add him to an email list and send him a welcome email). Upload and host your PDF file somewhere (like Dropbox or Titlegram) - this would let you generate a link to your PDF file. Then in the welcome email itself, you can insert the link in the email body to let your customers download the file. The reason you want to host it somewhere vs attach it is that most email providers don't like attachment, hosting it somewhere allows you to lessen the chance of being listed as a spam mail.
... View more