Xodo offers PDF viewing, annotation, and editing across web, desktop, and mobile platforms. The mobile apps are particularly well-regarded for their smooth rendering and responsive annotation tools. You can highlight text, draw, add comments, fill forms, and sign documents. The desktop version adds more editing capabilities and integrates with cloud storage services. The web version lets you view and annotate PDFs without installing anything.

Many of the core features are free, with a paid plan that adds advanced editing, conversion, and collaboration tools. Xodo is a good choice if you work with PDFs across multiple devices and want a consistent experience. The mobile apps are especially useful for reading and annotating on a tablet or phone, and they handle large files without lag.