Capturing open workbook as variable?

ThisWorkbook should refer to the workbook in which the macro is running.

You can declare a workbook variable:

dim wb as workbook

and then set that variable to a workbook using "Workbook.Open":

set wb = Workbook.Open(<fullpathandworkbookname>)

or you can select an already open workbook using its name

set wb = Workbooks(<yourworkbookname>)