If the organizer have chosen to issue invoices you will receive the invoice as a PDF together with the confirmation email when you buy the ticket(s). You will also be able to find it in the Transaction tab on Conferize.com/Mytickets together with all details of your transaction. These details are always available on this page regardless of invoices being issued or not.
If you need further documentation of the transaction or an invoice in case, that the organizer have chosen not to issue invoices, please contact the organizer. Find contact information on the ticket page or the event website.