This repository provides a fully-featured, cross-platform document reader and annotator for PDF, EPUB, and HTML snapshots, used as the core reading interface within the Zotero reference management ecosystem. It integrates PDF.js and EPUB.js for rendering, and a custom Structured Document Text (SDT) pipeline for cross-format search, reading mode (reflow), and read-aloud (TTS) with both browser-native and remote voice providers. The architecture is modular: a platform-agnostic common layer defines core abstractions (View, AnnotationManager, FocusManager, KeyboardManager, ReaderUI), with platform-specific bindings for Zotero desktop, web, iOS WebKit, and Android. The UI is built with React and features annotation tools (highlight, underline, note, ink, image, text), sidebar with thumbnails/annotations/outline, find-in-document via a web worker, and extensive keyboard navigation. Annotation management supports undo/redo, debounced saving, filtering, and export. The codebase demonstrates strong engineering practices with reusable design patterns (LRU cache, approximate string matching, navigation history, popup delay), but also contains large monolithic controller classes (Reader, PDFView) that handle many responsibilities. Overall, it is a high-quality, actively maintained application with sophisticated document processing capabilities.