通过php邮件函数发送pdf会导致打开错误

我附上了一个pdf文件，但附件没有在邮件中打开。 邮件服务器上出现以下错误

预期：application/pdf.pdf；找到：应用程序/x-empty

我有以下代码片段

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请帮我解决问题

检查内容类型是否与应用程序/pdfAlready相同，但相同的错误通过附加纯文本来测试代码file@MangeshSatheIND我尝试了文本文件，但得到了相同的错误我发现的是，有2个内容类型在您的代码。$filename是空的吗？

<?php
       $from='test1@domain.com';
       $to = 'test@domain.com'; 
    //define the subject of the email 
       $subject = 'Test email with attachment'; 
      $message='Startendday reports' ;
    //create a boundary string. It must be unique 
    //so we use the MD5 algorithm to generate a random hash 
       $file = file_get_contents('file.pdf');
       $content = chunk_split(base64_encode(file_get_contents($file)));
       $uid = md5(uniqid(time()));  //unique identifier
       $file_name='file.pdf';

       //standard mail headers
       $header = "From: ".$from."\r\n";
       $header .= "Reply-To: ".$to. "\r\n";
       $header .= "MIME-Version: 1.0\r\n";

       //declare multiple kinds of email (plain text + attch)
       $header .="Content-Type: multipart/mixed; boundary=\"".$uid."\"\r\n\r\n";
       $header .="This is a multi-part message in MIME format.\r\n";

       //plain txt part

       $header .= "--".$uid."\r\n";
       $header .= "Content-type:text/plain; charset=iso-8859-1\r\n";
       $header .= "Content-Transfer-Encoding: 7bit\r\n\r\n";
       $header .= $message. "\r\n\r\n";

       //attch part
       $header .= "--".$uid."\r\n";
       $header .= "Content-Type:application/octet-stream; name=\"".$file_name."\"\r\n";
       $header .= "Content-Transfer-Encoding: base64\r\n";
       $header .= "Content-Disposition: attachment; filename=\"".$file_name."\"\r\n\r\n";
       $header .= $content."\r\n\r\n";  //chucked up 64 encoded attch

       //sending the mail - message is not here, but in the header in a multi part
       if(mail($to, $subject, "", $header)) {
       echo "success";
       }else {
           echo "fail";
       }

?>