ThisWorkbook Property
The ThisWorkbook property returns the workbook where the Visual Basic code is running. In most cases, this is the same as the active workbook. However, if the Visual Basic code is part of an add-in, the ThisWorkbook property won’t return the active workbook. In this case, the active workbook is the workbook calling the add-in, whereas the ThisWorkbook property returns the add-in workbook.
Nguồn Microsoft 
