<div>
        <asp:Button ID="Button1" runat="server" Text="保存pdf文件" OnClick="Button1_Click" />
    </div>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using iTextSharp.text;
using iTextSharp.text.pdf;
using System.IO;

namespace Web
{
    public partial class WebForm2 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            try
            {
                //获取桌面路径设为文件下载保存路径
                string Fname = Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory)+"//证书.pdf";
                //Response.Write("<script>alert('桌面的路径是" + Fname + "');</script>");
//定义下载路径
                //string Fname = "C://Users//Administrator//Desktop//123.pdf";
                Rectangle pageSize = new Rectangle(1000, 500);
                Document document = new Document(pageSize, 10, 10, 120, 80);
                PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(Fname, FileMode.Create));
                document.Open();
                BaseFont bfChinese = BaseFont.CreateFont("C://WINDOWS//Fonts//simsun.ttc,1", BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED);
                iTextSharp.text.Font fontChinese = new iTextSharp.text.Font(bfChinese, 12, iTextSharp.text.Font.NORMAL, new iTextSharp.text.Color(0, 0, 0));

                //导出文本的内容：
                document.Add(new Paragraph("你好", fontChinese));

                //向PDF里面添加图片
                string imgurl = Path.GetFullPath("F:/项目/Web/Images/cp1.png");
                iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(imgurl);
                //SetAbsolutePosition方法是设置图片出现的位置
                img.SetAbsolutePosition(10, 100);
                writer.DirectContent.AddImage(img);
                document.Close();
                writer.Close();
                Response.Write("<script>alert('导出成功！');</script>");
            }
            catch (Exception ex)
            {
                throw ex;
            }
           
        }
    }
}