This repository is a mature Ruby gem (`pdf-reader`) that provides a comprehensive PDF parsing library. It implements a low-level PDF parser conforming to the PDF specification, enabling programmatic access to PDF content without rendering. The library supports text extraction (with UTF-8 conversion), metadata retrieval, page geometry, font handling (Type1, TrueType, Type3, CID), encryption (RC4, AES), and various PDF features like Form XObjects, inline images, and content stream processing. It is designed for document processing, text mining, and automated analysis of PDF files. The architecture follows a receiver/callback pattern for processing content streams, with `PDF::Reader` as the main entry point. Key modules include `PDF::Reader::Page` for high-level page access, `PDF::Reader::ObjectHash` for low-level object access, `PDF::Reader::Parser` for tokenization, and `PDF::Reader::Filter` for stream decompression. The library uses Sorbet for static type checking and includes a comprehensive test suite with over 120 spec files and numerous real-world PDF test fixtures. The codebase demonstrates solid engineering practices: clean abstractions (value objects like `Point`, `Rectangle`, `TextRun`), thread-safe caching (`SynchronizedCache`), optimized matrix operations (`TransformationMatrix`), and a pluggable width calculator system. It is actively maintained with support for multiple Ruby versions (2.1–4.0, JRuby, TruffleRuby) and has a well-documented changelog spanning over a decade of development.