PDFSharp write on more pages

I want to write a PDF on more than one page. I already created 4 pages, but the programm do a cut on the first page. So the page 2,3,4 are empty.

How to fix that?

Code:

string outFileName = "Vertrag/vertrag.txt";
                using (StreamWriter writer = new StreamWriter(outFileName, false, Encoding.UTF8))
                {
                    foreach (string inFileName in Directory.EnumerateFiles("schnippsel", "DE*.txt"))
                    {
                        using (StreamReader reader = new StreamReader(inFileName))
                        {
                            writer.Write(reader.ReadToEnd());
                        }
                    }
                }

                TextReader readFile = new StreamReader("Vertrag/vertrag.txt");

                PdfDocument pdf = new PdfDocument();
                PdfPage pdfPage = pdf.AddPage();
                PdfPage pdfPage2 = pdf.AddPage();
                PdfPage pdfPage3 = pdf.AddPage();
                PdfPage pdfPage4 = pdf.AddPage();

                XGraphics graph = XGraphics.FromPdfPage(pdfPage);
                XGraphics graph2 = XGraphics.FromPdfPage(pdfPage2);
                XGraphics graph3 = XGraphics.FromPdfPage(pdfPage3);
                XGraphics graph4 = XGraphics.FromPdfPage(pdfPage4);
                XFont font = new XFont("Verdana", 10, XFontStyle.Regular);

                string line = null;
                int yPoint = 0;

                while (true)
                {
                    line = readFile.ReadLine();
                    if (line == null)
                    {
                        break;
                    }
                    else
                    {

                        yPoint = yPoint + 40;
                        graph.DrawString(line, font, XBrushes.Black, new XRect(40, yPoint, 40, pdfPage.Height.Point), XStringFormats.TopLeft);
                    }
                }
                pdf.Save("Vertrag/vertrag.pdf");

                readFile.Close();
                readFile = null;

I must write more details here :P

It looks like that:

Page1: Hello, my name is Page 2: Page 3: Page 4: