You can find how to save a file here: how to save DOMPDF generated content to file?
$html =
'<html><body>'.
'<p>Put your html here, or generate it with your favourite '.
'templating system.</p>'.
'</body></html>';
$dompdf = new DOMPDF();
$dompdf->load_html($html);
$dompdf->render();
$output = $dompdf->output();
file_put_contents('Brochure.pdf', $output);
Sending email is very straight forward with CakeEmailL. Take a look here: http://book.cakephp.org/2.0/en/core-utility-libraries/email.html#sending-attachments
$Email = new CakeEmail();
$Email->from(array('me@example.com' => 'My Site'));
$Email->to('you@example.com');
$Email->subject('About');
$Email->attachments('/full/file/path/Brochure.pdf');
$Email->send('My message');