使用php函数sendmail发送带附件的邮件

i have a form like this :

this is 1.php

<form action="2.php" method="post">
Name: <input type="text" name="name" /></br>
Email: <input type="text" name="email" />
<input type="submit" value="Submit" />

than 2.php is like this :

<form action="3.php" method="post">
<input type="hidden" name="name" value="<?php echo $_POST['name'];?>"/>
<input type="hidden" name="email" value="<?php echo $_POST['email'];?>"/>
Telephone: <input type="text" name="telephone" /></br>
Location: <input type="text" name="location" />
<input type="submit" value="Submit" />

and the last one 3.php is like this:

<?php
    $error = "";
    if(isset($_POST['submit'])) {
        if(empty($_POST['email']) || empty($_POST['name'])) {
            $error .= 'There is an error. Retry.  <br />';
        }
        if(!filter_var($_POST['email'],FILTER_VALIDATE_EMAIL)) {
            $error .= 'E-mail is incorrect. <br />';
        }       
        function sendmail() {
            $to = 'user@domain.tld';
            $name = "Name : " .$_POST['name'];
            $telephone = "Telephone : " . $_POST['telephone']. "";
            $location = "Location : " .$_POST['location'];
            $subiect = "Form from webpage";
            $body = 'form content: '. $name. "
". $telephone. "

" . $location. "

". $from ;
            $from = "From: " . $_POST['email']. "";
            if(mail($to,$subiect,$body,$from)) {
              echo '<p>Thank you !</p><br />';
            }else{
              echo '<p>Error with server</p>';
            }
        }
        if($error == "") {
           sendmail();
        }
        echo "<p>".$error."</p>";
    }            
?>

My question is how can i introduce a <input type="file" name="file" id="file" /> in the 1st page when the user will be able to upload a photo and then on the 3.php page when he will hit the submit button that picture to be in the email

can anyone give me an example please ? Thank you !