Public Function LetzteDatei(ByVal Startdate As String, ByVal endDate As _
      String)
 
        Dim Path As String = "C:\SunnyWebBox\XML-Dateien"
        Dim lastFile As IO.FileInfo = Nothing
 
        With (New IO.DirectoryInfo(Path))
            For Each File As IO.FileInfo In .GetFiles
                With File
                    If .LastWriteTime >= Startdate AndAlso .LastWriteTime <= _
                      endDate Then
                        If IsNothing(lastFile) OrElse .LastWriteTime > _
                        lastFile.LastWriteTime Then
                            lastFile = File
                        End If
                    End If
                End With
            Next
        End With
 
    End Function

LetzteDatei(Now.AddDays(-300), Now.AddDays(1))
        MsgBox(lastFile.FullName)