The Run AutoCAD button allows to open the currently loaded DWG or DXF file with AutoCAD or DWGTrueView installed on the computer.
Quick Access Panel: 
Ribbon: Viewer -> Browse -> Run AutoCAD
Go to CADEditorX
URL of this topic:
https://it.cadsofttools.com/help/cadeditorx_ui_eng/index.html?external_cad_viewer.htm