Legal Question in Civil Litigation in California

The document that is served is given to the other parties. The proof of service is for the court, to know that you served it. It is "proof" of your "service." It gets filed with the court, not served again on your opponent.

The last page of every court paper that you file with the court, or that you serve on the other party, should contain a declaration of service, also called a "proof of service." Someone over 18 who is not a party to the action mails the document to everyone on the service list, and the document is then filed with the court. Usually the last page of the document is a signed proof of service, which is a legal shortcut since the person has obviously not yet served the document at the time it was put into the envelope for mailing. The court rules say the document that is served should be accompanied by an unsigned copy of the proof of service.

The original proof of service should go wherever the corresponding original document goes. That usually means it should be filed with the court. But when you serve a document that isn't filed (like, say written discovery), you should keep the original in your files.