A File Upload script in PHP

file-upload.php

<?php
 
if (isset($_POST['submit'])){
 
$pdfDirectory = "pdf/";
$thumbDirectory = "pdfimg/";
 
//get the name of the file
$filename = basename( $_FILES['pdf']['name'], ".pdf");
 
//remove all characters from the file name other than letters, numbers, hyphens and underscores
$filename = preg_replace("/[^A-Za-z0-9_-]/", "", $filename).".pdf";
 
//name the thumbnail image the same as the pdf file
$thumb = basename($filename, ".pdf");
 
    if(move_uploaded_file($_FILES['pdf']['tmp_name'], $pdfDirectory.$filename)) {
     
    //the path to the PDF file
    $pdfWithPath = $pdfDirectory.$filename;
     
    //add the desired extension to the thumbnail
    $thumb = $thumb.".jpg";
     
    //execute imageMagick's 'convert', setting the color space to RGB and size to 200px wide
    exec("convert \"{$pdfWithPath}[0]\" -colorspace RGB -geometry 200 $thumbDirectory$thumb");
         
    //show the image
    echo "<p><a href=\"$pdfWithPath\"><img src=\"pdfimage/$thumb\" alt=\"\" /></a></p>";
    }
}
 
?>
 
<form method="post" action="" enctype="multipart/form-data">
    <input type="file" name="pdf" />
    <input type="submit" name="submit" value="Upload" />
</form>