iTextSharp 设置 PDF 所有页面背景图功能

 在生成PDF 的时候，虽然可以在页面中设置背景图。

 但有些内容过长夸页面的时候，就很难设置背景图，变成了空白背景的页面！

 以下是重新生成每一页 PDF  背景图功能代码！

    public void SetPdfBackground(string pdfFilePath) 
    {
        //重新生成的 PDF 的路径
        string destFile = HttpContext.Current.Server.MapPath("sample.pdf");
        //create new pdf document
        FileStream stream = new FileStream(destFile, FileMode.Create, FileAccess.ReadWrite);

        PdfReader reader = new PdfReader(pdfFilePath);
        //read pdf stream 
        PdfStamper stamper = new PdfStamper(reader, stream);

        string imagePage = HttpContext.Current.Server.MapPath("../images/2012/bg2.png");
        System.Drawing.Image image = System.Drawing.Image.FromFile(imagePage);
        var img = Image.GetInstance(image, System.Drawing.Imaging.ImageFormat.Png);
        img.SetAbsolutePosition(0, 0);

        int totalPage = reader.NumberOfPages;
        for (int current = 1; current <= totalPage; current++)
        {
            var canvas = stamper.GetUnderContent(current);
            var page = stamper.GetImportedPage(reader, current);
            canvas.AddImage(img);
        }
        stamper.Close();
        reader.Close();
    }