十六进制到字符串PDF

I have a hexadecimal value that I need to convert back to a pdf and save it. I have tried to convert to string and display but browser keeps failing to load the pdf. I am retrieving the pdf from a web service and I know the hex is valid.

Below is the function I am using to convert and then to display:

header("Content-type: application/pdf");
header('Content-Disposition: inline; filename="test.pdf"');

function hex2str($func_string) {
$func_retVal = '';
$func_length = strlen($func_string);
for($func_index = 0; $func_index < $func_length; ++$func_index) $func_retVal .=    chr(hexdec($func_string{$func_index} . $func_string{++$func_index}));

return $func_retVal;
}

$hex = hex2str($string);

echo $hex;

Any help is greatly appreciated.