Before clicking the .exe , the engineer ensures their system meets the Autodesk requirements : a 64-bit processor (like an Intel Xeon or AMD Athlon 64) and at least 6GB of free disk space.

Since AutoCAD 2013 is by Autodesk (retired product), you cannot get it from official Autodesk servers. Possible sources:

After the installer finishes:

To protect their skyscraper's design from unauthorized modifications, the engineer uses the new security features in Service Pack 1.1 , controlling how custom LISP scripts run within the application. Why This Specific Version Matters

Autocad 2013 English Win 64bit Exe 'link' Guide

Before clicking the .exe , the engineer ensures their system meets the Autodesk requirements : a 64-bit processor (like an Intel Xeon or AMD Athlon 64) and at least 6GB of free disk space.

Since AutoCAD 2013 is by Autodesk (retired product), you cannot get it from official Autodesk servers. Possible sources: AutoCAD 2013 English Win 64bit Exe

After the installer finishes: