Try this..
This will capture the filename
The Pattern is given below
/fileName=(.+?)\"/
<?php
$subject = "<!doctype html> <html> <head> <meta charset="utf-8"> <title>Formatting the report</title><meta http-equiv="refresh" content="5;url=/file/xslt/download/?fileName=somename.pdf"> </head>";
$pattern = '/fileName=(.+)"/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 2);
print_r($matches);
?>
$1->Contains the file name