Private Sub openPDFToolStripMenuItem_Click(ByVal sender As System.Object, _
      ByVal e As System.EventArgs) Handles openPDFToolStripMenuItem.Click
        Dim PrfOeffnen As New OpenFileDialog()
        PrfOeffnen.Title = "PDF öffnen"
        PrfOeffnen.Filter = "PDF-Dateien (*.pdf)|*.pdf|Alle Dateien (*.*)|*.*"
        PrfOeffnen.ShowDialog()
    End Sub