Technically you don't. Only the original complaint and summons require an affidavit of service to be filed with the court. Our service rules are long, meandering and the method (the service) can be denied by the served party. "Everyone" uses the sheriff or a licensed process server.
Where are you? I very much doubt that you need a process server to file your answer.
In addition to the original filing, only in the initial response by the defendant ("entering the case") does almost everyone use a process server or the sheriff to avoid any chance of a claim of default. After that, attorneys may even email but usually won't accept that from a pro se. Regular mail with proper postage affixed and an affidavit of that at the bottom of each filing is sufficient. If I want to speed things up, I email a copy to the OP attorney, with a statement that it's also in the mail.
It's rules 7-9, and no one I know likes them. IMHO they need to be cleaned up. LINK
Yeah, I blew that. My bad. I should have refreshed my memory about the specifics of the states involved.If you go out of the state and are involved in a car accident, the lawsuit would normally belong in the state where the accident occurred. But here we seem to be talking about an allegation of intentional conduct intended to harm a resident of Pennsylvania within the State of Pennsylvania. We don't have the full facts so we can't make a full analysis, but it's quite possible that the case is properly in Pennsylvania under the aforementioned long arm statute.