QCAD is primarily an open-source (GPLv3) application designed for 2D drafting. However, the DWG format is proprietary, making it difficult to support directly within an open-source core. To provide this functionality, QCAD utilizes a built on the Teigha libraries from the Open Design Alliance.
While the QCAD DWG plugin is a reliable and robust solution, users may encounter some issues. Here are some common issues and troubleshooting tips: qcad dwg plugin