The most versatile free JavaScript PDF library — pdf-lib is a pure-JavaScript (no native dependencies) MIT-licensed engine that runs in both the browser and Node.js and uniquely both creates new PDFs AND modifies existing ones: draw text, vector paths, and images; embed fonts; fill and read AcroForm fields; merge, split, rotate, copy, and remove pages; and add attachments. Modern TypeScript-first async API, ~7k+ GitHub stars, actively maintained by Hopding. No paid tier, no SaaS — install with npm and use it forever.