PDFsam (PDF Split And Merge) is a mature, open-source desktop application for PDF manipulation. It provides tools for splitting, merging, rotating, extracting pages, alternate mixing, inserting backpages, and splitting by size or bookmarks. The architecture is a modular JavaFX GUI monolith built on Java 25 with preview features. Communication is event-driven via a custom EventStudio bus, and dependency injection uses a custom injector with Jakarta annotations. PDF processing relies on the Sejda SDK. The application supports workspace persistence, theming, internationalization (30+ languages), automatic updates, and a premium tool marketplace. It is packaged for Windows (MSI, MSIX), macOS (DMG), and Linux (DEB). The codebase demonstrates solid engineering with clear module boundaries, extensive unit and UI tests, and reusable UI components. However, it carries technical debt from a large custom event surface, a non-standard DI framework, and some deprecated property handling.