There are ~10 independent PDF engines. We built another one.

KeyPDF was developed over around 14 months, and we achieved true editing of the text with preservation of fonts, alignments, and overall structure. KeyPDF is written mostly in JS with WebAssembly modules for parsing to achieve the highest speed of processing, as all files loaded in KeyPDF are local and computed on the client device. KeyPDF is unique because existing tools have a tradeoff: some genuinely edit PDFs but only by processing them on a server, while the ones that run locally in the browser can't truly edit but rely on adding annotations on top, basic page manipulations, and form filling. KeyPDF does both at once: real editing, fully on-device, which makes it not only fast and private but also fully portable and accessible from any device. The way we achieved it is by choosing to start from scratch. Currently, there isn't a single free JavaScript PDF engine capable of editing PDF files directly, only expensive commercial SDKs. pdf.js can only view and annotate; jsPDF can only write new PDF files; neither can really edit existing text or remove objects, as that isn't the primary function of either. The KeyPDF engine was built on the idea of bringing editing capabilities directly to the browser without reliance on any server backend, and after many months of work, it is publicly available at keypdf.net.