I have both Inventor and AutoCAD installed. I have set file associativity to use Inventor for DWG files.
![SEC_CAD_0-1706051977689.png SEC_CAD_0-1706051977689.png](https://forums.autodesk.com/t5/image/serverpage/image-id/1317588iF39A59E6D2F7C3D4/image-size/medium?v=v2&px=400)
If I have Inventor open and double-click an IPT file in Explorer then that part opens in a new tab in the current instance of Inventor.
If I double-click a DWG file in Explorer it opens a new instance of Inventor.
If I double-click another DWG file I again get a new instance of Inventor. Task Manager now shows 3 instances of Inventor running.
![SEC_CAD_1-1706052010365.png SEC_CAD_1-1706052010365.png](https://forums.autodesk.com/t5/image/serverpage/image-id/1317589i51FADCA3A90B7F1D/image-size/medium?v=v2&px=400)
I don't think that this is the correct behaviour.