<?php
$im = new Imagick();
try {
    $im -> readImage("doc.pdf[5]");
    $im -> destroy();
} catch (ImagickException $e) {
    echo "Error: " . $e -> getMessage() . "\n";
}

$im = new Imagick();
try {
    ob_start();
    @$im -> readImage("doc.pdf[5]");
    ob_end_clean();
    $im -> destroy();
} catch (ImagickException $e) {
    echo "Error: " . $e -> getMessage() . "\n";
}