About duplex printing issue at vendor side

Hi,

Currently , when I execute my program,it generates PDF attachment ,and for printing I have set the duplex settings in Smartform in which first page contains details of material and back side of first page contains the Terms and condition . I have also set my printer settings in my printer, and when I open and print that PDF documents in my printer,it shows perfectly in the single page but when vendor opens it , terms and condition does not come on the back side of the first page, so how can i solve that issue?what changes to be needed from developer side to overcome this issue?

Thanks in advance.