How can a recipient attach material to a completed fillable PDF jotform and return it to me?

I could see that this is a duplicate thread. Your request is already handled in your previous thread: https://www.jotform.com/answers/1927395.

As explained in the above thread, you can use you online (web) form and create a notification email so that you receive an email whenever the form is submitted - Setting-up-Email-Notifications.