About PDF Studio

Why it exists

Most online PDF tools upload your file to a server, process it there and send it back. That is a poor fit for contracts, bank statements, medical letters and anything else you would rather not hand to a stranger. PDF Studio started as a self-hosted tool and was rebuilt so that the processing happens on your own device instead. There is nothing to sign up for, nothing to pay and no ads.

How it works

The site is a set of static pages. When you use a tool, proven open-source PDF engines compiled to WebAssembly run in background workers in your browser: pdf.js for rendering and text, pdf-lib for building pages, qpdf for encryption and lossless compression, and PDFium with MozJPEG for image compression. See the privacy page for exactly what runs where and what is stored.

Open-source licences

Everything we ship uses permissive licences (MIT, BSD, Apache 2.0, ISC, zlib, the FreeType License and the SIL Open Font License). We do not ship copyleft code, fonts or data. The full list of components and their licence texts is on the licences page.

Supported browsers and devices

Current versions of Chrome, Edge, Firefox and Safari on desktop are fully supported. Phones and tablets work too, but large jobs need a lot of memory, so we show a warning above about 200 MB or 1,000 pages.

Known limits

• Changing a PDF writes a new file, which invalidates existing digital signatures.
• Merging drops the source files' bookmarks and form fields for now; rebuilding bookmarks is planned.
• Compressing to a target size may be impossible for PDFs that are mostly text; you then get the smallest file we could make.
• A drawn or typed signature image is not a cryptographic digital signature.
• The site runs on free hosting with no uptime guarantee. Once the app has loaded, the core tools keep working offline.