Hello,
Try this:
$client = new Pdfcrowd("***", "***");
$client->setPageMargins(".5in", ".2in", ".5in", ".2in");
$client->setHeaderHtml("<b>This is a header</b>");
$client->setFooterHtml("<i>Page %p out of %n</i>");
$pdf = $client->convertHTML(stringHTML);