pdf-lib
pdf-lib is a free, open-source, pure-JavaScript library for creating and modifying PDF documents that runs identically in Node.js and directly in the browser (no server round-trip needed), which distinguishes it from most PDF libraries that depend on native bindings or a backend service. It can create new PDFs from scratch, or — notably — load and modify existing PDF files: filling form fields, adding pages, embedding images, drawing text/shapes onto existing pages, and merging multiple PDFs into one.
Because it has zero native dependencies, pdf-lib works in edge/serverless runtimes (Cloudflare Workers, Deno, browser Web Workers) where libraries requiring a native binary often fail to run, making it a common choice for lightweight PDF manipulation inside modern JAMstack or serverless architectures. Filling out an existing PDF form (a common requirement for government or bank forms distributed as fillable PDFs) is one of its most-used capabilities — form fields can be read and populated programmatically without needing the original design source file.
For Nigerian developers building a client-side tool to fill out a bank form, generate a certificate, or merge multiple uploaded PDFs entirely in the browser (avoiding a server round-trip and associated latency/cost), pdf-lib's browser-native, zero-dependency design is its main advantage over server-only libraries like PDFKit.