About Lemmafour

Most online PDF tools work by uploading your file to someone else's server, processing it there, and sending a result back. That model is fine for a flyer — and unacceptable for a contract, a medical record, a salary slip, or an ID scan. Lemmafour exists to remove that trade-off: professional PDF tools where the document never leaves your device.

How it works

Lemmafour compiles a full PDF engine to WebAssembly and runs it inside your browser. Opening, editing, merging, compressing, signing, and exporting all happen locally. There is no upload step to remove — the architecture simply doesn't have one for your document bytes.

The editor is built around a principle we call surgical editing: when you change one word, we change the bytes for that word — the rest of your document's content, fonts, and structure pass through untouched. Many editors re-generate whole paragraphs or pages, which can subtly change spacing, fonts, and appearance. Lemmafour's output is verified against a rendering engine so what you saw is what you saved.

What you can do today

• Edit text directly in existing PDFs, with reflow and style matching.
• Merge, split, organize, rotate, insert, and delete pages.
• Compress PDFs and convert between images and PDF.
• Fill forms, sign, stamp, add text and images, remove watermarks.
• Prepare documents for print with margin, size, and color checks.

Fonts and attributions

Lemmafour bundles open-licensed fonts (DejaVu under the Bitstream Vera license; Liberation, Noto, Source, Fira, Inter and other families under the SIL Open Font License 1.1) for its interface and for text you add to documents. Each family's license text ships alongside the font files in this site's assets. We are grateful to their designers and maintainers. The engines and libraries Lemmafour is built on are credited on the open source page.

Get in touch

Found a bug, a document that renders wrong, or a feature you need? We genuinely want the file (well — a non-sensitive reproduction of it). Say hello via the contact page.