Any party serving discovery shall file a. Any party serving discovery shall file a certificate of service of discovery document.{Amended April 22, 2013}. Local rules shall not require the filing of discovery. Instead, a party serving discovery shall file a certificate of service of discovery document. Any party serving discovery shall file a certificate of service of discovery document. Ill. (b) Certificate of Service. All Illinois Courts must accept these forms. Discovery is used to gather information from another party in your case. Learn how and when to use it.