For a personal user focused on organization and project management, choose Obsidian. Its ability to store notes locally ensures your data remains private, and its Markdown support enables flexible formatting. However, be prepared for a learning curve and note that it lacks real-time collaboration features — ideal for individual use rather than team environments.
On the other hand, if you're in a business setting requiring secure and efficient PDF processing, Stirling-PDF is the better option. Its open-source nature and capabilities for handling high document volumes suit organizations needing robust document management. However, keep in mind that the costs can accumulate with usage and that its mobile functionality is limited, making it less ideal for those who require a fully-featured mobile app.