Problem with PDO INSERT

Hello friends I am very lay in PDO and would like the help of friends to try to create an INSERT that would register a font name in the BD font table. Next, I created this code below, based on the UPDATE code that is working:

    <form name="enter" method="post" action="" enctype="multipart/form-data">
    <?php
    if(isset($_POST['enter'])){
    $pdo = new PDO('mysql:host=localhost;dbname=site', "root", "");
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $stmt = $pdo->prepare ('INSERT INTO fontes (font) VALUES (:font)');
    $stmt->execute(array(':font' => $font));

    echo 
    "<meta http-equiv='refresh' content='0; URL= ../cadastros/cad_fonte.php'>
    <script language='javascript'>
    window.alert('Dados alterados com sucesso!');
    </script>";
    }
    ?>

    <h3>Caso a fonte desejada não esteja listada, cadastre-a agora!</h3><br />

    <input type="text" name="font" value="" />
    <input type="submit" name="enter" value="Cadastrar" />

I ask your friends to help me make a code that works so that I can register.

Thank you in advance.