iTextSharp对现有的PDF进行加密

[xjzdr]

用iTextSharp对现有的PDF进行加密，总搞不定，要么加密后的文件为空了(原来是有内容的)，或者出现问题：The document has no pages.(再打开PDF时错误：出现共享违规)
我的代码如下：

protected void btnEncryption3_Click(object sender, EventArgs e)
{
iTextSharp.text.Document document = new Document(PageSize.A4, 50, 50, 50, 50);
string PdfPath = AppDomain.CurrentDomain.SetupInformation.ApplicationBase;
PdfPath = PdfPath + "PDFFiles\\";
string PdfFIle = PdfPath + "004.PDF";
try
{


PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(PdfFIle, FileMode.Open));

writer.SetEncryption(PdfWriter.STRENGTH128BITS, "userpass", "ownerpass", PdfWriter.AllowCopy | PdfWriter.AllowPrinting);


document.Open();


document.Close();
}
catch (Exception de)
{
Console.Error.WriteLine(de.Message.ToString()+de.StackTrace);
//document.Close();
}

}

说明：我把 document.Open();


document.Close();
这两句去了，也不行，加上 writer.Close();也不行。

请做过、用过的大侠们把这段代码贴出来呀，帮帮忙。

[xjzdr]

用过的同僚们，请把代码整出来看看呀

[子夜__]

using System;
using System.Collections.Generic;
using System.Text;
using iTextSharp.text.pdf;
using System.IO;

namespace PDFSecurity
{
    class PDFEncry
    {
        public static void Encry(string pdfSrc, string pdfDest, bool strength,
            string userPassword, string ownerPassword, int permissions)
        {
            PdfReader reader = new PdfReader(pdfSrc);
            Stream os = (Stream)(new FileStream(pdfDest, FileMode.Create));
            PdfEncryptor.Encrypt(reader, os, strength, userPassword, ownerPassword, permissions);
        }
    }
}

代码很少。

[amovingsun]

楼上代码少却功能实现的很充分，顶

[imfor]

绑定！