$file = CFile::MakeFileArray(
    $_SERVER['DOCUMENT_ROOT'].'/upload/payment/'.$_GET['ORDER_ID'].'.pdf',
    false,
    false,
    ''
);

$fileSave = CFile::SaveFile(
    $file,
    '/payment',
    false,
    false
);

CEvent::Send(
    'SEND_PAY_PDF',
    's1',
    array('EMAIL_TO' => $USER->getEmail()),
    'N',
    '',
    array($fileSave),
    'ru'
);