word file edit

[dizyn]

I am trying this code to edit word file, it works fine if the both strings are same lenght but not if both are of different length.

any help

<?PHP
$tmp=	file_get_contents("work.doc");
$tmp = str_replace ("sys" , "asd",$tmp);
$tmp=	file_put_contents("work2.doc" , $tmp);
?>