There are two methods, which provide saving changes to the PDF document. These are
Zend_Pdf::save($filename, $updateOnly = false) saves the PDF document to a file. If $updateOnly
is true, then only the new PDF file segment is appended to a file. Otherwise, the file is overwritten.
Zend_Pdf::render($newSegmentOnly = false) returns the PDF document as a string. If
$newSegmentOnly is true, then only the new PDF file segment is returned.