I really don't see why there are 3 workbooks involved, that might even increase the likelihood of errors.

And you definitely shouldn't be using 2 instances of Excel.

Anyways, if you want to be able to pick the Monthly Report file you should take a look at Application.GetOpenFilename.

That would show a dialog where the user can navigate to and select the file.

It returns the file name of the selected file which you can then open.