When you want to use an UDF or procedure in several workbooks, then save it
into a module of Personal Macro Workbook (Personal.xls, it's created
automatically, when you select Personal Macro Workbook as destination to
save a newly-created macro, and later is loaded automatically whenever you
start Excel).
One way:
You can also create a Reference between the two workbooks (if they are both
open) from the Tools Menu. To make the reference, both the files should be
open. After that, only the workbook you are using has to be open.