Hi,
Thank you for your message.
I believe he wants to retrieve the document and that depends on how those documents are connection to each other. If you you are using Linked documents thats it rather easily to get linked document Info, but if you dont then how the system would know which product belongs to which? You could also use Related document to establish some kind of connection or have custom table storing the connections there.
Let us know if you ahve further questions.
Kind regards,
Richard Sustek