This report presents a conceptual framework developed by the PID4NFDI to advance metadata interoperability, harmonization, and technical integration of Persistent Identifier (PID) infrastructures in the German National Research Data Infrastructure (NFDI). Building upon the groundwork laid during the initialization phase and guided by the vision outlined in the integration phase proposal. Our approach integrates insights from community surveys, interviews with use case partners, and extensive engagement with NFDI consortia members.