The Occupancy Certificate (OC) is a document that proves that the property being purchased is in compliance with all building codes and regulations. The OC should be supplied to the buyer by the builder or developer at the time of purchase, but it's easy to forget to ask for this important certificate. The Achievement Certificate is an important state document that allows the builder to apply for an OC. If the structure is not finished in accordance with building codes and regulations, the establishment may reject the OC application.