zedgraph quality inside PDF Doc depend on PageSize.A4.Rotate

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For using you will need this two dll, I'm sure everybody knows that, but its probally the best.
http://sourceforge.net/projects/zedgraph/files/
http://sourceforge.net/projects/itex...es/itextsharp/
(this example use itextsharp-4.1.6 )

My Question
THe following Code will make a Graph, create a Bitmap, and start Adobe-Reade to present the Graph inside.
The whole code works fine. I only have trouble, when I use this line:
Dim Doc As New iTextSharp.text.Document (iTextSharp.text.PageSize.A4.Rotate())

instead of this line:
Dim Doc As New iTextSharp.text.Document(iTextSharp.text.PageSize.A4, 10, 10, 10, 10)

The quality of of the whole Picture is not good then.
Eventhough when I change width and hight for the Rectangle.
Then I tried to change the Bitmap width and hight, but in that case nothing happends?
Does anybody know a way, to handle the quality for using why nothing happends, when I change hight or width in this line:
Dim Doc As New iTextSharp.text.Document(iTextSharp.text.PageSize.A4, 10, 10, 10, 10)

Imports ZedGraph
Imports iTextSharp
Imports iTextSharp.text.pdf

Private Sub btnOrgPDFtrans_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOrgPDFtrans.Click
        'Create Graph pane
        Dim w As Integer = 600
        Dim h As Integer = 400
        Dim myPane As New GraphPane(New Rectangle(0, 0, w, h), "", "", "")

        ' Set the titles and axis labels
        myPane.Title.Text = "My Bar Chart"
        myPane.XAxis.Title.Text = "Day"
        myPane.YAxis.Title.Text = ""

        ' Add random data
        Dim list As New PointPairList()
        Dim rand As New Random()
        Dim i As Integer
        For i = 0 To 15
            Dim x As Double = CDbl(i) + 1
            Dim y As Double = rand.NextDouble() * 1000
            list.Add(x, y)
        Next i

        ' Create Bar Chart
        Dim myCurve As BarItem = myPane.AddBar("", list, Color.Blue)
        Dim colors As Color() = {Color.Red, Color.Blue}
        myCurve.Bar.Fill = New Fill(colors)
        myCurve.Bar.Fill.Type = FillType.Solid
        myCurve.Bar.Fill.RangeMin = 0
        myCurve.Bar.Fill.RangeMax = 4
        myPane.Chart.Fill = New Fill(Color.White, Color.FromArgb(220, 220, 255), 45)
        myPane.Fill = New Fill(Color.White, Color.FromArgb(255, 255, 225), 45)

        'Create Bitmap
        Dim bm As Drawing.Bitmap = New Bitmap(1, 1)
        Dim g As Graphics = Graphics.FromImage(bm)
        myPane.AxisChange(g)

        ' Create PDF file
        Dim Doc As New iTextSharp.text.Document(iTextSharp.text.PageSize.A4.Rotate())
        Dim writer As iTextSharp.text.pdf.PdfWriter
        writer = PdfWriter.GetInstance(Doc, New FileStream("Chap0610.pdf", FileMode.Create))

        ' Open PDF file for write
        Doc.Open()
        Dim cb As PdfContentByte = writer.DirectContent

        ' Write Chart/image to PDF file
        Dim im As iTextSharp.text.Image
        im = iTextSharp.text.Image.GetInstance(myPane.GetImage(), Drawing.Imaging.ImageFormat.Bmp)
        im.SetAbsolutePosition(50.0F, 80.0F)
        cb.AddImage(im)

        ' Close PDF document
        Doc.Close()
        g.Dispose()
        'Open PDF Application
        Process.Start("Chap0610.pdf")
    End Sub

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