Open both the source and destination workbooks. Then open the
VBA Editor. In the Project Explorer window (typically on the
left side of the screen), drag the module containing the code
from the source project to the destination project.
If you export the module from the VBA editor you can reimport into another
sheet or you can copy and paste it.
But if you have a common macro, why not put it in the personal workbook or
create a template with the macros in it that can be used for new workbooks.
Lots of options, so it does depend on how and to what extent you need to do
this?