At the top of the page, try doing something like this:
<?php
header("Location: http://blah.com/path/to/your.pdf");
exit;
?>
This may or may not fix your problem, but I highly recommend it over using meta refresh tags.
If this still causes you problems, my next recommendation would be to have your PHP file create headers for the PDF content type and then passing the file through to the user.
I'm not sure of the content type needed for PDF files, but you would use this at the top of the page before echoing the PDF file to the user, but this code is for jpegs... you need to replace it with the proper content type:
<?php
header("Content-type: image/jpeg");
?>
Goodluck.