解码十六进制PDF并作为电子邮件附件发送

Question

我必须解码以下代码，然后将其作为PDF附加到C＃的电子邮件中。

using (var stream = new MemoryStream())
using (var writer = new StreamWriter(stream))    // using UTF-8 encoding by default
using (var smtpClient = new SmtpClient("localhost", 25))
using (var message = new MailMessage("Mail@mail.com", "me@mail.com", "Just testing", "See attachment..."))
{
    writer.WriteLine("0x255044462D312E340A25E2E3CFD30A332030206F626A203C3C2F4[...]");
    writer.Flush();
    stream.Position = 0;     // read from the start of what was written

    System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Application.Pdf);
    Attachment attach = new Attachment(stream, ct);
    message.Attachments.Add(new Attachment(stream, "filename.pdf", "application/pdf"));

    smtpClient.Port = 25;
    smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
    smtpClient.UseDefaultCredentials = false;
    smtpClient.Host = ConfigurationManager.AppSettings["MailHost"];
    smtpClient.Send(message);
}

已发送电子邮件，但是当我要打开它时，它告诉我文件已损坏。

有人对PDF文件进行了这种解码吗？