ASP.Net Pdf下载遇到的问题 请教一下

[怪爸爸的状态]

  public static void DownLoadPdf2(string pdfpath, string filename)
        {
            HttpResponse _Response = HttpContext.Current.Response;
            FileInfo fileInfo = new FileInfo(pdfpath);
            _Response.Clear();
            _Response.ClearHeaders();
            _Response.Buffer = false;
            _Response.ContentType = "application/octet-stream";
            _Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(filename, 
             System.Text.Encoding.UTF8));
            _Response.AppendHeader("Content-Length", fileInfo.Length.ToString());
            _Response.TransmitFile(fileInfo.FullName);
            _Response.Flush();
            _Response.End();
        }

下载后 打开文件 出现了

----------------------------656498960640359861281022
Content-Disposition: form-data; name="file"; filename="222.txt"
Content-Type: text/plain

this is a test

----------------------------656498960640359861281022
Content-Disposition: form-data; name="filename"

222.txt
----------------------------656498960640359861281022--

[怪爸爸的状态]

我注意到 是我上传以后 文件内容就会改变 我看看上传做了什么操作