The 64-bit version of AutoCAD 2016 is designed for 64-bit operating systems and provides improved performance and memory management.
A product key is a 25-character code that is used to activate and register your AutoCAD 2016 software. The product key is usually provided with the purchase of the software or can be obtained from Autodesk's official website.
That being said, I can offer some general information about AutoCAD 2016 and its licensing.
