Assuming Mac VBA is similar to PC VBA then the following should work. The code assumes column A contains the document names in question
Code:
Sub RemoveDuplicates()
Dim LastRow As Long
Dim i As Long
LastRow = Cells(Rows.Count, "A").End(xlUp).Row
For i = LastRow To 2 Step -1
If Left(Cells(i, 1), 18) = Left(Cells(i - 1, 1), 18) Then
Rows(i).Delete Shift:=xlUp
End If
Next i
End Sub