通过邮件获取错误的pdf文件大小

如何解决通过邮件获取错误的pdf文件大小

我正在发送一个 278kb 的 pdf 文件，但我收到了一个无法打开的 5kb 文件......我不明白问题出在哪里......这是我的代码：

 MailMessage oMail = new MailMessage();
            string base64String = "";
            using (WebClient client = new WebClient())
            {
                var bytes = client.DownloadData(pdfUrl);
                  base64String = Convert.ToBase64String(bytes);
            }
            var fileName = FileName;                
            MemoryStream strm = new MemoryStream(Convert.FromBase64String(base64String));                
            Attachment data = new Attachment(strm,fileName);           
            oMail.Attachments.Add(data); 
            oMail.From = new MailAddress(from);
            oMail.To.Add(new MailAddress(to));
            oMail.Subject = subject;
            oMail.Body = body;          
            SmtpClient oServer = new SmtpClient("XXX.XXX.XX.XXX");
            oServer.Port = **;
            oServer.EnableSsl = false;
            
                oServer.Send(oMail);