URL blocking with iptables

we have internal network 192.168.129.x for a system hosted with
pdf.xxx.xyz URL is already public accessible
but when try to connect as site (/ap/p.nt) of the URL pdf.xxx.xyz/ap/p.nt
restriction to be applied publicly except accessing internally
can anyone guide me on this??

Do you still need help on this? If so, please take the time to re-word your question. I understood that you want to access a document on your internal network, where the document is already available on an external web server. But that's all I understood.