Product fields not usaThankble in PDF Template

Hi,

We have created some fields in Products as following
$aos_name
$aos_address
$aos_city and so on

We are trying to use these fields in PDF template.

If we use each of these fields once, the PDF template renders and the generated PDF has all the values perfectly
If we try using any of these fields more than once, the generated PDF contains values as $aos_name, $aos_address, etc. and not the values for these fields.

Kindly help resolving the same.

Thanks & Regards,
Kunal Kishor Ugale