Congrats on selling your tickets. To upload a PDF, login to your StubHub account and in the upper right hand corner select sales under the My ticket sdrop down. It will default to show you any upen sales with a button to select/upload your PDF. You will have to upload the file and make sure to designate which page of your PDF is which seat number.
Once completed, you should get an email regarding the buyer getting their tickets and your payment being processed. Remember to double check your PDF and make sure it matches the tickets you sold.
You can either upload the PDF of your ticket or once you have the ticket, place in the barcode and stubhub and create the ticket for you and have your buyer be able to download it at home!