Process flow of (PR) attachments from third-party system

Dear SAP Community,

We currently have the following scenario at hand.

A third party system will be used to create Purchase Requisitions, which then have to replicated into the local S/4 System and then the Central Procurement Hub. The more dedicated question is: What is the flow of PR Attachments which are attached within the third-party system and then replicated into the local S/4 system?

What is the best practice if the PR is created within a third-party system? How are the attachments processed and especially, where are they stored?

I would highly appreciate your support!

Best,

Thomas