For those with original installation discs or USB drives, the serial number is usually printed on a label on the external packaging or the sleeve. System Requirements for 2016 Installation

Civil 3D – How to find your serial number - ARKANCE UK Community

Before attempting to use your serial number for a new installation, ensure your hardware meets the minimum standards for this version:

AutoCAD Civil 3D 2016: Finding Your Serial Number and Product Key

Every Autodesk product requires a unique product key that identifies the specific software and version being installed. It is important to note that the product key for a standalone product differs from the key used if that same product is part of a larger suite.