Open workbook, insert copied rows VBA code

maybe

Sub ContractorsTab()
   Dim rCopy as Range
   Dim wb as workbook
   Set rCopy = Selection
   set wb = Workbooks.Open(Filename:="X:\OSC DETAIL\Invoices Sent to AP\Sent Invoice Summary - 2012.xlsx")
    rCopy.Copy
    wb.Sheets("Contractors").Rows("4:4").Insert Shift:=xlDown
    Windows("OS Invoices 07-15.xlsm").Activate
End Sub