Below is a sample code base to convert PDF files to HTML5 template making use of well known tool Crocdoc :

$_product = $observer->getProduct();
        $productid=$_product->getId(); 
        $read = Mage::getSingleton('core/resource')->getConnection('core_read');
          $query = 'SELECT link_file,link_url from downloadable_link where product_id='.$productid; 
        $results = $read->fetchAll($query);
        if($results[0]['link_file']||$results[0]['link_url']){
        if($results[0]['link_file']) {
            $l1=$results[0]['link_file'];
            $link=Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_MEDIA).'downloadable/files/links'.$l1;

        } else {
            $l1=end(explode('/',$results[0]['link_url']));
            $link=Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_MEDIA).'downloadable/files/'.$l1;
        }

        Mage::log($link);
        error_reporting(E_ALL);
        $exampleApiToken = 'AXa5RgV6MDQzm9tbKZJYepqI';

        if (php_sapi_name() != 'cli') {
                header('Content-Type: text/plain');
        }

        $ExternalLibPath=Mage::getModuleDir('', 'Pack_Book') . DS . 'lib' . DS .'Crocodoc.php';
        require_once ($ExternalLibPath);
        $que = 'SELECT * from catalog_product_response where product_id='.$productid; 
        $results1 = $read->fetchAll($que);
        $update=0;
        if($results1[0]['product_id'])
            $update=1;
        //Mage::log($results1[0]['uuid']);
        Crocodoc::setApiToken($exampleApiToken);
        $uuid = null;

        try {
                $uuid = CrocodocDocument::upload($link);
                $write = Mage::getSingleton("core/resource")->getConnection("core_write");
                if($update==0)
                    $query1 = 'INSERT INTO catalog_product_response VALUES ('.$productid.',"'.$uuid.'")'; 
                else
                    $query1 = 'update catalog_product_response set uuid = "'.$uuid.'" where product_id='.$productid; 
                $write->query($query1);
                return ;
        } catch (CrocodocException $e) {
                return ;
        }
        return  ;