FBReader is a complimentary electronic book application designed to organize and display digital publications saved on your device. The application supports numerous popular ebook formats, with primary compatibility for ePub files (including full ePub functionality), Amazon Kindle azw format (also recognized as mobi), and FictionBook fb2 format delivered as compressed archives. Additional file types accommodated include Rich Text Format, Microsoft Word documents, HTML pages, and plain text documents. DjVu format support requires installation of a complimentary plugin. Accessing PDF documents and comic book archives necessitates either a complimentary plugin or upgrading to FBReader Premium. The premium version involves a single payment, granting unlimited access to all advanced features. The reading functionality operates independently without requiring internet connectivity, allowing offline use. When connected to a network, users gain access to extensive digital book collections offering both complimentary and purchasable titles. Pre-configured libraries featuring content in English, French, Russian, and Polish languages are readily available. Users may also incorporate personalized OPDS catalog feeds according to their preferences. Alternatively, digital content can be acquired through external sources and imported directly into the application. FBReader provides synchronization capabilities through the Book Network service, which operates on Google Drive infrastructure. This feature maintains consistent library data, bookmark collections, and reading progress across multiple devices. Synchronization remains disabled initially; configuration is available through the preferences settings menu. The application offers integration with numerous third-party dictionary applications, encompassing Dictan, ColorDict, Fora Dictionary, FreeDictionary.org, and LEO dictionary services. The premium version includes enhanced functionality with integrated Google Translate support. The application delivers efficient performance with extensive personalization options. Users may install external TrueType or OpenType font collections and define custom background appearances. Display brightness adjustments are accessible by sweeping vertically along the screen's left margin. Multiple display themes optimized for daytime and nighttime reading conditions are available for selection.