Application.ThisWorkbook Property (Excel)
Returns a Workbook object that represents the workbook where the current macro code is running. Read-only.
Use this property to refer to the workbook that contains your macro code. ThisWorkbook is the only way to refer to an add-in workbook from inside the add-in itself. The ActiveWorkbook property doesn't return the add-in workbook; it returns the workbook that's calling the add-in.
The Workbooks property may fail, as the workbook name probably changed when you created the add-in. ThisWorkbook always returns the workbook in which the code is running.
For example, use code such as the following to activate a dialog sheet stored in your add-in workbook.
This property can be used only from inside Microsoft Excel. You cannot use it to access a workbook from any other application.