server/lib/private/preview/pdf.php

<?php
/**
 * Copyright (c) 2013 Georg Ehrke georg@ownCloud.com
 * This file is licensed under the Affero General Public License version 3 or
 * later.
 * See the COPYING-README file.
 */
namespace OC\Preview;

if (extension_loaded('imagick') && count(@\Imagick::queryFormats("PDF")) === 1) {

	class PDF extends Provider {

		public function getMimeType() {
			return '/application\/pdf/';
		}

		public function getThumbnail($path, $maxX, $maxY, $scalingup, $fileview) {	
			$tmpPath = $fileview->toTmpFile($path);

			//create imagick object from pdf
			try{
				$pdf = new \imagick($tmpPath . '[0]');
				$pdf->setImageFormat('jpg');
			} catch (\Exception $e) {
				\OC_Log::write('core', $e->getmessage(), \OC_Log::ERROR);
				return false;
			}

			unlink($tmpPath);

			//new image object
			$image = new \OC_Image($pdf);
			//check if image object is valid
			return $image->valid() ? $image : false;
		}
	}

	\OC\Preview::registerProvider('OC\Preview\PDF');
}