const sFolder As String = "D:\data\"
const Pattern As String = "*.pdf"
Dim strFile As String
Dim i As Integer
Dim coll As New Collection
strFile = Dir(sFolder & Pattern)
While strFile <> ""
coll.Add strFile
strFile = Dir()
Wend
For i = 1 To coll.Count
Name sFolder & coll.Item(i) As sFolder & Format(Date(), "mmmyyyy") & "_" & Format(i, "000") & ".pdf
Next