I checked with the PDF file this time downloading it instead of viewing it within the FireFox browser and there were no wierd characters.
So this issue is with only FireFox inline viewer. Is there anything I can do to troubleshoot this ?
header('Content-type:application/pdf');
header('Content-Disposition:attachment;filename="'.$bp->Name.'.pdf"');
# header('Content-Disposition:inline;filename="'.$bp->Name.'.pdf"');