The audit trail collects and logs all of the changes made to a contract.
It can be found at the bottom of the contract. Click on the bar marked "View audit trail" to open the audit trail.
Here you can see a collected "history" of the contract from start to finish. If you click "Show details" you can see the exact change that was made. If you click the underlined time you will see the exact date and time of the edit.
The audit trail is considered a part of the contract and is added to the contract PDF in its entirety.