The General Data Protection Regulation (GDPR) introduces stringent data protection standards across the European Union, emphasizing user consent, data minimization, and privacy-by-design principles. This development explains compliance challenges and solutions for Public Knowledge Project (PKP) applications until OJS 3.3, including Open Journal Systems (OJS), Open Monograph Press (OMP), and Open Preprint Systems (OPS), in the context of GDPR. Software Developments in Technischer-Informatiosnbibliothek (TIB) as partner of the CRAFT-OA project, a collaborative initiative aimed at advancing Diamond Open Access publishing, has integrated GDPR compliance measures for PKP applications. Key issues identified include insufficient cookie consent mechanisms, inadequate user data access and erasure tools, and non-compliance risks posed by third-party services. Addressing these challenges, OJS version developments by TIB 3.5 introduces features such as an invitation-based user workflow, enhanced role management, and improved privacy controls. These developments underscore the importance of aligning software infrastructure with regulatory requirements to foster secure and ethical data practices in scholarly publishing.