解决方法

<%@ WebHandler Language="C#"%>
using System;
using System.Web;
using iTextSharp.text;
using iTextSharp.text.pdf;

public class lockPdf : IHttpHandler {
  public void ProcessRequest (HttpContext context) {
    HttpServerUtility Server = context.Server;
    HttpResponse Response = context.Response;
    Response.ContentType = "application/pdf";
    using (Document document = new Document()) {
      PdfWriter writer = PdfWriter.GetInstance(
        document,Response.OutputStream
      );
      writer.SetEncryption(
// null user password => users can open document __without__ pasword
        null,// owner password => required to __modify__ document/permissions        
        System.Text.Encoding.UTF8.GetBytes("ownerPassword"),/*
 * bitwise or => see iText API for permission parameter:
 * http://api.itextpdf.com/itext/com/itextpdf/text/pdf/PdfWriter.html
 */
        PdfWriter.ALLOW_PRINTING
            | PdfWriter.ALLOW_copY,// encryption level also in documentation referenced above        
        PdfWriter.ENCRYPTION_AES_128
      );
      document.open();
      document.Add(new Paragraph("hello world"));
    }
  }
  public bool IsReusable { get { return false; } }
}

PdfReader reader = new PdfReader(INPUT_FILE);
using (MemoryStream ms = new MemoryStream()) {
  using (pdfstamper stamper = new pdfstamper(reader,ms)) {
    // add your content
  }
  using (FileStream fs = new FileStream(
    OUTPUT_FILE,FileMode.Create,FileAccess.ReadWrite))
  {
    PdfEncryptor.Encrypt(
      new PdfReader(ms.ToArray()),fs,null,System.Text.Encoding.UTF8.GetBytes("ownerPassword"),PdfWriter.ALLOW_PRINTING
          | PdfWriter.ALLOW_copY,true
    );
  }  
}

using System;
using System.Diagnostics;
using System.Drawing;
using System.IO;
using System.Windows.Forms;
using Newtonsoft.Json;
using iTextSharp.text;
using iTextSharp.text.pdf;
using it = iTextSharp.text;
using System.Drawing.Imaging;
 
        //打印确认表
        private void Btn_print_Click(object sender, EventArgs e)
        {
            string path = Application.StartupPath + "\\PDFs";
            if (!Directory.Exists(path))
            {
                Directory.CreateDirectory(path);
            }
            //使用微软雅黑字体，解决中文无法显示，注意msyh.ttc后面的,0是必须的
            BaseFont baseFont = BaseFont.CreateFont(Application.StartupPath + "\\Fonts\\msyh.ttc,0", BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED);
            it.Font font = new it.Font(baseFont, 14, it.Font.BOLD, it.BaseColor.BLACK);
            using (var doc1 = new Document(PageSize.A4, 5, 5, 35, 5))
            {
                PdfWriter.GetInstance(doc1, new FileStream(path + "\\Doc1.pdf", FileMode.Create));
                doc1.Open();
                //生成条形码
                var bmp = ZXingHelper.GenerateBarcode("12345678900000");
                var txm = it.Image.GetInstance(System.Drawing.Image.FromHbitmap(bmp), ImageFormat.Bmp);
                //txm.ScalePercent(24f);
                txm.ScaleAbsoluteHeight(40);
                txm.SetAbsolutePosition(doc1.PageSize.Width - 220, doc1.PageSize.Height - 32);
                doc1.Add(txm);//把条形码放到页面右上角
 
                PdfPTable table = new PdfPTable(7);
 
                PdfPCell cell = new PdfPCell(new Phrase("X X X X 验 证 意 见 确 认 处 理 记 录 表", font))
                {
                    Colspan = 7,
                    Border = 0,
                    MinimumHeight = 30,
                    HorizontalAlignment = 1
                };
                table.AddCell(cell);
 
                it.Font fontCell = new it.Font(baseFont, 10, it.Font.NORMAL, it.BaseColor.BLACK);
                float[] cellWidths = new float[] { 10, 35, 35, 45, 40, 65, 40 };
                table.SetWidths(cellWidths);
 
                cell = new PdfPCell(new Phrase("县区：          XX：          XX：           XXXX：               日期：   月     日          时间：        ", fontCell))
                {
                    Colspan = 7,
                    Border = 0,
                    HorizontalAlignment = 0,
                    MinimumHeight = 15
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("座\r\n号", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5,
                    MinimumHeight = 35
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("姓 名", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("xx号", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("XX（通过/未通过/未验证）", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("XXXX（采集/未采集）", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("验证意见（XX/XX/XXXX/XXXX）", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                cell = new PdfPCell(new Phrase("XXXX确认处理情况）", fontCell))
                {
                    HorizontalAlignment = 1,
                    VerticalAlignment = 5
                };
                table.AddCell(cell);
 
                for (var i = 1; i < 31; i++)
                {
                    table.AddCell(new PdfPCell(new Phrase(i.ToString(), fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5,
                        MinimumHeight = 17
                    });
                    table.AddCell(new PdfPCell(new Phrase("正大·光明龑", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                    table.AddCell(new PdfPCell(new Phrase(" ", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                    table.AddCell(new PdfPCell(new Phrase(" ", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                    table.AddCell(new PdfPCell(new Phrase(" ", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                    table.AddCell(new PdfPCell(new Phrase(" ", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                    table.AddCell(new PdfPCell(new Phrase(" ", fontCell))
                    {
                        HorizontalAlignment = 1,
                        VerticalAlignment = 5
                    });
                }
 
                fontCell = new it.Font(baseFont, 12, it.Font.NORMAL, it.BaseColor.BLACK);
                cell = new PdfPCell(new Phrase("XXXXX签字：                                               XXXXX丙签字：                        ", fontCell))
                {
                    Colspan = 7,
                    Border = 0,
                    MinimumHeight = 20,
                    HorizontalAlignment = 0
                };
                table.AddCell(cell);
 
                it.Font fontFooter = new it.Font(baseFont, 10, it.Font.NORMAL, it.BaseColor.BLACK);
                PdfPCell cellFooter = new PdfPCell(new Phrase("说明：1.文字描述文字描述文字描述文字描述文字描述文字描述文字描述\r\n2、文字描述文字描述文字描述文字描述文字描述文字描述文字描述文字描述文字描述文字描述；3、文字描述文字描述文字描述文字描述文字描述文字描述文字描述文字描述，存档备查。", fontFooter))
                {
                    Colspan = 7,
                    Border = 0,
                    MinimumHeight = 40,
                    Left = 0,
                    PaddingLeft = 0,
                    HorizontalAlignment = 0//0=Left, 1=Centre, 2=Right
                };
                table.AddCell(cellFooter);
                doc1.Add(table);
                doc1.Close();
            }
            if (MessageBox.Show("生成成功，是否打印？", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
            {
                Spire.Pdf.PdfDocument pdf = new Spire.Pdf.PdfDocument(path + "\\Doc1.pdf"); 
                pdf.Print();
            }
 
        }

public static IntPtr GenerateBarcode(string barcode)
        {
            BarcodeWriter writer = new BarcodeWriter();
            writer.Format = BarcodeFormat.CODE_128;
            writer.Options = new ZXing.Common.EncodingOptions
            {
                Height = 100,
                Width = 200,
                PureBarcode = false
            };
 
            Bitmap bitmap = writer.Write(barcode);
            return bitmap.GetHbitmap();
        }