BricsCAD is a highly compatible AutoCAD alternative. While not portable, it has a tiny footprint and can be installed on a portable SSD quickly. It reads .dwg files perfectly.
Autodesk does not officially release "Portable" versions of AutoCAD. Most portable packages found online are modified by third parties, which often violates the End User License Agreement (EULA). Security Hazards: Portable.Autodesk.AutoCAD.2010
It runs directly from a USB drive or a local folder without writing to the Windows Registry. BricsCAD is a highly compatible AutoCAD alternative