افزودن تمبر صفحه به PDF از طریق C#

public static void AddPageStamp()
{
    String inputFileName = "sample-4pages.pdf";
    String outputFileName = "AddPageStamp_out.pdf";
    String pageStampFileName = "PageStamp.pdf";
    Document document = new Document(_dataDir + inputFileName);

    PdfPageStamp bluePageStamp = new PdfPageStamp(_dataDir + pageStampFileName, 1);
    bluePageStamp.setHeight(800);
    bluePageStamp.setBackground(true);

    PdfPageStamp plumPageStamp = new PdfPageStamp(_dataDir + pageStampFileName, 2);
    plumPageStamp.setHeight(800);
    plumPageStamp.setBackground(true);

    for (int i = 1; i < 5; i++)
    {
        if (i % 2 == 0)
            document.getPages().get_Item(i).addStamp(bluePageStamp);
        else
            document.getPages().get_Item(i).addStamp(plumPageStamp);
    }

    document.save(_dataDir + outputFileName);
}