I've used dompdf with some success before. Although it can be a bit fussy about malformed HTML and there are still some CSS methods that aren't supported (e.g. css float does not work).
Download the package from github, and place it into a folder called dompdf in your application/thirdparty directory.
You can then create a helper with some functions to use the dompdf library, here is an example:
dompdf_helper.php :
<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
function pdf_create($html, $filename='', $stream=TRUE)
{
include APPPATH.'thirdparty/dompdf/dompdf_config.inc.php';
$dompdf = new DOMPDF();
$dompdf->load_html($html);
$dompdf->render();
if ($stream) {
$dompdf->stream($filename.".pdf", array("Attachment" => 0));
} else {
return $dompdf->output();
}
}
You simply pass the pdf_create method your HTML as a string, the filename for the pdf file it will generate, and then an optional thirdparameter. The third parameter is a true/false flag to determine if it should save the file to your server before prompting the user to download it or not.