For personal organization and project management, choose Obsidian. Its customizable nature and local storage ensure privacy, making it perfect for users who prioritize control over their data. However, be prepared for a learning curve and avoid it if you require real-time collaboration or prefer cloud-centric solutions.
On the other hand, if you work in a business environment that needs secure, high-volume PDF processing, go with Stirling-PDF. Its open-source foundation and robust security features cater well to organizations dealing with sensitive documents. Just be aware that costs can accumulate with a paid processing model and mobile app functionality may be limited, making it less ideal for those seeking a fully-featured mobile experience.