It is important to clarify what you are downloading. AutoCAD is not a parametric, history-based modeler like SolidWorks or Fusion 360. You do not "build" a part by sketching a profile and extruding it with editable parameters that you can tweak five steps later.
Instead, AutoCAD offers
The days of walking into a store to buy a CD-ROM are gone. Today, the "AutoCAD 3D download" is a digital process managed entirely through Autodesk.