It looks like you're looking for a write-up related to AutoCAD Mechanical 2012 (64-bit) and its Product Key.
Alternatively, purchase an Autodesk Industry Collection subscription (currently ~$2,655/year) which includes the modern AutoCAD Mechanical (2024/2025), but note that Autodesk no longer sells 2012 licenses. You can also search for legitimate resellers selling old perpetual licenses (rare and risky).
: For legitimate licenses, you can find your unique serial number by signing into your Autodesk Account and checking the Products & Services
Since this software was released in 2011, there are a few things to keep in mind for 64-bit systems:
System Requirements
Processor: AMD Athlon 64, AMD Opteron, Intel Xeon with Intel EM64T support, or Intel Pentium 4 with Intel EM64T support (all must support SSE2 technology).