VS 2008 - Zedgraph Quality Inside PDF Depend On PageSize A4 Rotate

For using you will need this two dll, I'm sure everybody knows that, but its probably the best.
[URLs] (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? Any way, to handle the quality for using why nothing happens, when I change height 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
[Code] .....