- preg_replace: documentation ( source)
<?php
$re = '/(.*?)(\[\w{3}=\')(\w+\.\w+)(\'\])(.*?)(\[\w{3}=\')(\w+\.\w+).*/s';
$str = 'Hello, view this pdf [PDF=\'hello.pdf\']
and then view this PDF [PDF=\'goodmorning.pdf\']';
$subst = '$1 <object data=\\"https://myurl.com/media/$3\\" class=\\"pdf-shortcode-iframe" type=\\"application/pdf\\"> <iframe class=\\"pdf-shortcode-iframe\\" src=\\"https://docs.google.com/viewer?url=https://myurl.com/media/$3&embedded=true\\"></iframe> </object>$5 <object data=\\"https://myurl.com/media/$7\\" class=\\"pdf-shortcode-iframe\\" type=\\"application/pdf\\"> <iframe class=\\"pdf-shortcode-iframe\\" src=\\"https://docs.google.com/viewer? url=https://myurl.com/media/$3&embedded=true"></iframe> </object>';
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;