There are many solution to convert HTML to PDF, I can suggest you the one by https://grabz.it.
The have a flexible PHP API which can be used by cronjobs or directly from PHP web page.
If you want to try it, at first you should get an app key + secret for authorization and the development free SDK
Here is an example of a basic implementation.
//First init
include("GrabzItClient.class.php");
// Create the GrabzItClient class
// Replace "APPLICATION KEY", "APPLICATION SECRET" values for your account!
$grabzIt = new GrabzItClient("Application Key", "Application Secret");
// To take a PDF screenshot
$grabzIt->URLToPDF("http://www.google.com");
// To save in case public callback handler is available
$grabzIt->Save("http://www.example.com/handler.php");
// OR To save in case public callback handler is not available,
// it's a synchonous method can be usedthe will force your application to wait
// while the screenshot is created
$filepath = "images/result.jpg";
$grabzIt->SaveTo($filepath);
It's possible to get other kinds of screenshots such as image screenshot and etc.
