asp.net 下载pdf ，下载后的大小与实际大小不一样

代码是这样子的，从数据库读取文件的长度没问题，但浏览器下载后总是不一样？请问会是什么原因？

 SqlDataReader dr = cmd.ExecuteReader(System.Data.CommandBehavior.SequentialAccess);
                    if (dr.Read())
                    {
                        string filename = dc + " + " + dr["filename"].ToString();
                        int length = int.Parse(dr["leng"].ToString());
                        Context.Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8));
                        Context.Response.AddHeader("Content-Transfer-Encoding", "binary");
                        //if (filename.EndsWith("pdf"))
                        //{
                        //    Context.Response.ContentType = "application/pdf";
                        //}
                        //else
                        //    Context.Response.ContentType = "application/x-msdownload";//"application/octet-stream"application/x-msdownload;
                        Context.Response.ContentType = "application/octet-stream";


                        int bufferSize = 1024000;

                         int bytesRead;
                         long readFrom = 0;
                         do
                         {
                             byte[] bytes = new byte[bufferSize];
                             bytesRead = (int)dr.GetBytes(3, readFrom, bytes, 0, bufferSize);

                             //Response.BinaryWrite(bytes);
                             Response.OutputStream.Write(bytes, 0, bytesRead);
                             Response.Flush();
                             readFrom += bufferSize;
                         } while (bytesRead == bufferSize);

加content-length响应头试试。。

 Response.AddHeader("content-length",length.ToString());