<?php
$resource = $_GET [ 'src' ] ; // здесь вовзращается путь в стиле /upload/iblock/81/example.pdf
header ( "Content-type: application/pdf" ) ; header ( 'Content-Disposition: attachment; filename="' . $file [ 'basename' ] . '"' ) ;
readfile ( $_SERVER [ 'DOCUMENT_ROOT' ] . $resource ) ;
PD9waHAKCiRyZXNvdXJjZSA9ICRfR0VUWydzcmMnXTsgLy8g0LfQtNC10YHRjCDQstC+0LLQt9GA0LDRidCw0LXRgtGB0Y8g0L/Rg9GC0Ywg0LIg0YHRgtC40LvQtSAvdXBsb2FkL2libG9jay84MS9leGFtcGxlLnBkZgokZmlsZSA9IHBhdGhpbmZvKCRyZXNvdXJjZSk7CmhlYWRlcigiQ29udGVudC10eXBlOiBhcHBsaWNhdGlvbi9wZGYiKTsKaGVhZGVyKCdDb250ZW50LURpc3Bvc2l0aW9uOiBhdHRhY2htZW50OyBmaWxlbmFtZT0iJyAuICRmaWxlWydiYXNlbmFtZSddIC4gJyInICk7CgpyZWFkZmlsZSgkX1NFUlZFUlsnRE9DVU1FTlRfUk9PVCddIC4gJHJlc291cmNlKTsK