FBReader vs Mozilla PDF.js

FBReader is an ebook reader for Windows, macOS, Linux, Android, and iOS. It opens formats including ePub, fb2, mobi, HTML, RTF, and plain text, as well as ePub books protected with Readium LCP. Its Book Network can synchronize collections, reading positions, bookmarks, and custom shelves across supported devices. Books in the network are stored in the user's Google Drive space, while metadata, covers, and reading positions are stored on FBReader servers.

Online OPDS book catalogues are supported on Android, Windows, macOS, and Linux; iOS support is planned. Android Premium adds PDF and comics support, Google and DeepL translation integration, and automatic reading aloud. The free iOS version is limited to ten books and disables online translators. FBReader offers free plans for desktop, Android, and iOS; Android Premium is $14.99 as a one-time purchase. The company says its current code is closed source.

Mozilla PDF.js is a free, web standards-based platform for parsing and rendering PDF files. Developers can use its display API to render documents and retrieve information, or adapt the viewer layer for a custom interface. That viewer is used in Firefox and project browser extensions. PDF.js renders annotations and supports adding a subset of annotation types, and it supports form filling; OCR is not provided. The project targets HTML5-compliant browsers and includes a legacy build for older browsers, although PDF feature support varies by browser and version. Prebuilt builds are available, with hosted copies listed through jsDelivr, cdnjs, and unpkg. Developers can clone and build it locally, but some browsers require a local web server instead of opening PDFs through file URLs. Cross-origin requests are blocked by default, so CORS or a server proxy may be needed. For large documents, rendering only visible pages can reduce memory use. PDF.js is licensed under Apache 2.0.