PDF.js
Mozilla's open-source JavaScript PDF renderer — the engine behind Firefox's built-in PDF viewer and most browser-based PDF preview tools.
PDF.js is a JavaScript library created at Mozilla to render PDFs directly in a web browser without any external plugins. Originally built because Mozilla wanted Firefox to display PDFs natively (instead of relying on Adobe's plugin), PDF.js has grown into the industry-standard browser-based PDF renderer. Chrome, Edge, and many PDF viewer apps all use it under the hood.
What PDF.js does
- Parses PDF structure — reads the content streams, fonts, images, and metadata
- Renders pages to canvas — draws the visual output pixel-perfect in a browser canvas element
- Extracts text content — returns each text run with its coordinates, font, and size
- Loads incrementally — streams and renders long PDFs progressively so users see early pages quickly
PDF.js vs pdf-lib
These two libraries complement each other and PDF Genie uses both:
- PDF.js reads and renders (input side)
- pdf-lib creates and modifies (output side)
For tools that need to show a PDF page — previews, thumbnails, PDF to JPG, OCR PDF — PDF.js does the rendering. For tools that need to change a PDF — Merge, Split, Watermark — pdf-lib handles the writing.
Licensing
PDF.js is Apache 2.0 licensed, which is what makes it viable for commercial products. Mozilla maintains it publicly on GitHub and ships updates alongside Firefox releases. It's genuinely battle-tested — billions of PDFs have been rendered through it over the years.