by person who has a process service license

What is Service of Process?
Service of Process is when legal documents such as summonses, complaints, subpoenas, writs and other court documents are delivered to the individual to whom the legal document is directed. Service of Process must be served by an individual who is not a party to the case.

What does a Process Server do?
A legal process server delivers (or serves) legal documents to a defendant or an individual involved in a court case. The process server must serve the documents in accordance with the legislation in the area of service. This may mean handing the documents to the defendant personally or sub-serving to someone in the same household or business. Once the documents are delivered, the process serving agent must provide proof that the papers were served. This is done through a document call an Affidavit of Service, also called a Proof of Service, which must be notarized and given to the party who requested service.

Process servers will also file your papers with the courts, can do document retrieval and may offer various types of investigations: skip trace, people locates, surveillance, etc.
http://www.serve-now.com/about-process-serving