the Workbook event you're looking for is the AddinInstall event - it gets called when the workbook is installed as an addin
in the
VB ide, double-click the special "ThisWorkbook" class of your project, and then select the built-in Workbook object from the list in the top-left combo box. In the top-right drop-down you'll see listed all the events that you can capture for the Workbook object
similarly, you may want to think about moving away from the Auto_Open macro procedure and using the Workbook's "Open" event instead
check the on-line help, or search the web - there are plenty of examples there