stop snippet processing

$token = '~!@MyToken~!@';

switch ($modx->event->name) {
    case 'OnParseDocument':
        $resource->_output = str_replace('[[', $token, $resource->_output );
        break;

    case 'OnWebPagePrerender':
        $resource->_output = str_replace($token, '[[', $resource->_output);
        break;
}

<?php
switch ($modx->event->name) {
    case 'OnParseDocument':
	  if (! function_exists('quote_meta') ) {
		function quote_meta($a) {
		  $lhs = array("[", "]");
		  $rhs = array("091X2", "092X2");
		  $b = str_replace("&", "\46", $a[2]);  //save "&"
		  $lhs_preg = array('|<!(!*)notag>|',  '|<!(!*)/notag>|');
		  $rhs_preg = array('<$1notag>',  '<$1/notag>');
		  $b = preg_replace($lhs_preg, $rhs_preg, $b);
		  $b = str_replace($lhs, $rhs, $b);
		  return str_replace("\46", "093X", $b);
			  }
		  }
	  $output =& $modx->documentOutput;
	  $output = preg_replace_callback("#(<notag>)(.*?)(</notag>)#s", "quote_meta", $output);
	break;
    case 'OnWebPagePrerender':
	  $output = &$modx->resource->_output; // get a reference to the output
	  $output = str_replace('091X2','[',$output);
	  $output = str_replace('092X2',']',$output);
	  $output = str_replace('093X','&',$output);
	break;
}

<?php
if (!defined('MODX_CORE_PATH'))  { define('MODX_CORE_PATH', '/PATH_TO_CORE/'); }
if (!defined('MODX_CONFIG_KEY')) { define('MODX_CONFIG_KEY', 'config'); }
require_once( MODX_CORE_PATH . 'model/modx/modx.class.php');
$modx = new modx();
$modx->initialize('mgr');
//=============================

// Validate user membership & session
$user = $modx->getUser();
if ( ($user->isMember('Administrator') || $user->isMember('Editors')) && $user->hasSessionContext('mgr') )
{
	$id = $_GET['id'];
	$table = str_replace( 'modx', 'custom', $modx->getOption('table_prefix') ) . files;
	$sql = "SELECT `file_name`, `file_size`, `file_type`, `file_data` FROM `$table` where `id`=$id LIMIT 1" ;
	$query = $modx->query($sql);
	
	if ($query) { $row = $query->fetch(PDO::FETCH_ASSOC); }
	$name = $row['file_name'];
	$size = $row['file_size'];
	$type = $row['file_type'];
	$file = $row['file_data'];
	
	//header("Content-Disposition: attachment; filename=$name"); //Uncomment for download otherwise browser opens PDF in beowser
	header("Content-length: $size");
	header("Content-type: $type");
	echo $file;		
}
?>