The following function returns True or False depending on whether the
workbook name passed to it is an open or closed workbook:
Public Function bIsBookOpen(ByRef szBookName As String) As Boolean
On Error Resume Next
bIsBookOpen = Not (Application.Workbooks(szBookName) Is Nothing)
End Function
Sub Demo()
MsgBox "Is MyBook.xls open? " & bIsBookOpen("MyBook.xls")
End Sub