Option Explicit
Sub myTest()
Dim strFn As String, strEx As String
Dim strSp As String, arrSp() As String
Dim arrNb() As String, x As Long, z As Long
Dim strLt As String, arrLt() As String, i As Long
ChDir "E:\VBA\2018\Oktober"
strEx = ".pdf"
strSp = "_"
strLt = "-"
strFn = Dir("*" & strEx)
Do While Len(strFn) > 0
If InStr(strFn, strLt) = 0 Then
z = 0: i = 0
arrSp = Split(Replace(strFn, strEx, ""), strSp)
For x = LBound(arrSp) To UBound(arrSp)
If IsNumeric(arrSp(x)) Then
ReDim Preserve arrNb(0 To z)
arrNb(z) = arrSp(x)
z = z + 1
Else
ReDim Preserve arrLt(0 To i)
arrLt(i) = arrSp(x)
i = i + 1
End If
Next x
On Error Resume Next
Name strFn As Join(arrNb, strSp) & strLt & Join(arrLt, strLt) & strEx
On Error GoTo 0
End If
strFn = Dir
Loop
End Sub