The transition from siloed paper archives to digital ecosystems is vital for aligning heritage research with Open Science. At the Royal Institute for Cultural Heritage (KIK-IRPA), the H-SEARCH project modernizes 75 years of interdisciplinary intervention dossiers, spanning conservation and material science, by migrating disparate formats into a unified framework of machine-actionable FAIR Digital Objects (FDOs). This initiative addresses the challenges of a heterogeneous data landscape characterized by inconsistent metadata and limited interoperability. To resolve these issues, KIK-IRPA established a stepwise pre-archival workflow that first consolidates legacy and born-digital dossiers into a controlled "pre-archive" environment. This foundational stage organizes disparate data to prepare for the current transition toward embracing fully-realised Digital Objects. Methodologically, this involves implementing over 40 data models aligned with international standards within the Cordra repository. This architecture links archival metadata to institutional and external platforms, ensuring long-term preservation according to OAIS principles while enhancing data discoverability. Metadata created in Cordra are fed back into the pre-archive, where the archival workflow starts. Digital files and their metadata are then bundled, preserved, and stored in a dedicated long-term preservation environment, ensuring that the data remain accessible, reliable, and reusable over time. Finally, these FDOs are shared via the BALaT+ platform, which integrates multiple institutional data sources. While the project promotes "as open as possible" access, it employs structured metadata and tiered controls to manage sensitive administrative and personal data in compliance with GDPR. Ultimately, H-SEARCH demonstrates how rigorous metadata schemas can maintain data privacy and integrity while contributing to a transparent, FAIR-compliant scientific record