Skip to content
QPDF.ca

Your PDFs stay private

QPDF works with your documents inside your own web browser. This page explains, in plain English, what happens to a file when you use a QPDF tool, what does and does not travel over the internet, and how you can check it for yourself.

The short version

  • QPDF’s tools process your PDF on your device, inside the browser tab.
  • Your documents are not uploaded to QPDF’s servers or sent to any other service.
  • QPDF has no accounts, no analytics, no advertising and no tracking cookies.
  • You can check this yourself: load a tool, switch off your Wi-Fi, and process a file.

What “browser-local” processing means

Most online PDF services ask you to upload your document. Their servers make the change and you download the result, so a copy of your file has travelled to — and at least briefly lived on — someone else’s computer.

QPDF turns that around. When you open a tool, your browser downloads the software needed to do the job. When you then select a PDF, the browser reads it from your disk into memory and the software works on it right there, using your own processor. The finished file is created in memory and saved back to your device. There is no QPDF processing server, because none is needed.

How JavaScript and WebAssembly do the work

Web browsers can run two kinds of program: JavaScript, and WebAssembly — a compact format that lets mature programs written in languages like C, C++ and Rust run inside a web page at close to native speed. QPDF uses both. Depending on the tool, the work is done by well-established open-source engines:

  • pdf-lib and PDF.js for reading, editing and rendering pages;
  • qpdf for encryption, decryption and structural repairs;
  • PDFium and Hyper Compress for editing and compression;
  • CoherentPDF for merging with bookmarks and attachments;
  • PyMuPDF (running on Pyodide) and Ghostscript for conversions and PDF/A;
  • Tesseract for OCR (English and French).

Every one of these engines is served from QPDF’s own hosting, at a pinned version. QPDF does not load scripts, fonts or engines from third-party content networks, and the site’s Content Security Policy instructs your browser to refuse connections to any origin other than QPDF’s own.

Downloading software is not uploading documents

Your browser does talk to qpdf.ca — but only in one direction for anything that matters. It downloads web pages, styles, scripts and WebAssembly engines, exactly as it would for any website. It never uploads your PDF, its contents, or its file name. Think of it like downloading a word processor and then writing a letter on your own computer: the company that made the software never sees the letter.

What happens to your file, step by step

1. When you select a PDF

You choose a file with the file picker or drag it onto the page. The browser gives the page read access to that one file. QPDF reads its bytes into memory. Nothing is sent over the network, and the file name is used only to suggest a name for the result.

2. While it is processed

The tool runs in the page or in a background Web Worker so the page stays responsive. Workers are part of the same browser tab and do not create network connections to send your data anywhere.

3. When you download the result

The output is assembled in memory and handed to your browser’s download feature through a temporary blob: address that exists only inside your browser. The file is written to your device. QPDF keeps no copy.

Temporary memory in your browser

While you work, your document and intermediate data live in the tab’s memory, and the page may create preview images of pages. This data is released when you clear the tool, process another file, or close the tab. Be aware of the limits: browsers decide when memory is actually freed and overwritten, and your operating system may write memory to a swap or hibernation file. QPDF cannot securely erase memory on your device.

What QPDF stores in your browser

QPDF never stores your documents, their file names or text extracted from them. It does store:

  • Favourite tools — the list of tools you starred (Compress PDF by default), in localStorage.
  • Interface settings — such as layout preferences, keyboard shortcuts and PDF viewer display preferences.
  • Application files for offline use — QPDF’s own pages, scripts and engines, cached by a service worker so tools can work without a connection.
  • Downloaded fonts — fonts used to build OCR text layers may be cached in IndexedDB so they do not need to be downloaded again.

All of this stays in your browser and is never sent to QPDF. You can remove it at any time by clearing this site’s data in your browser settings.

What still reaches the hosting infrastructure

QPDF is a static website hosted on Cloudflare Pages. Like any website, loading it means your browser requests files from Cloudflare’s servers. Those requests necessarily reveal ordinary technical information — your IP address, the pages and files requested, and your browser’s user agent — which Cloudflare may process to deliver and protect the site. These requests contain QPDF’s software, never your documents.

Some tools need large engines (for example PyMuPDF, about 54 MB). The first time you use one, your browser downloads it from qpdf.ca; the tool page tells you before it does so. QPDF does not use analytics or advertising services, so there are no requests to such services.

Don’t just trust us. Test it yourself.

You can confirm that QPDF does not need to upload your file, in about a minute:

  1. Open qpdf.ca while you are connected to the internet.
  2. Choose Compress PDF, Merge PDF or another supported tool.
  3. Wait until the tool shows “Ready to work offline”. This means its processing software has finished loading. For tools with large engines, select Download for offline use first.
  4. Disconnect your computer from Wi-Fi or unplug the network cable.
  5. Select a PDF from your device.
  6. Process it as usual.
  7. Download the finished document.

If the tool can process your PDF while your computer is disconnected from the internet, it demonstrates that the operation does not require uploading your document to a remote processing server.

For a closer look, open your browser’s developer tools, select the Network tab, and watch it while you process a file: no request carries your document. This simple test is a useful check, but it does not replace a comprehensive, independent security audit.

Which tools work offline?

Every published QPDF tool processes documents locally. Each tool page shows its offline status near the top:

  • Ready to work offline — everything the tool needs is stored in your browser.
  • Works offline after a one-time download — tools that use a large engine (PyMuPDF, Ghostscript, Tesseract OCR) let you download it first, then work offline.

Offline use requires a browser that supports service workers, and it will not work in some private-browsing modes. If a site update is released while you are offline, the tool keeps using the version you already have.

The limits of local processing

Browser-local processing removes the biggest risk — sending your document to someone else — but it cannot make an unsafe device safe:

  • Your device’s security matters. Malware, a compromised operating system or a shared computer can expose documents regardless of the tool you use.
  • Browser extensions can read web pages. Extensions with permission to “read and change data on all websites” could in principle read what a page is working on. Use a private window or a clean browser profile for very sensitive work.
  • Downloads stay on your device. Results are saved to your downloads folder, where other people or programs with access to your device can find them.
  • Memory has limits. Very large files can exceed the memory available to a browser tab, especially on phones.
  • Check important results. Always verify redactions, signatures and conversions before relying on them.

Open source and honest claims

QPDF is free software released under the GNU Affero General Public License and built on the open-source BentoPDF project. Anyone can read the source code to see how it handles files. QPDF has not been independently audited and holds no security certifications; we describe what the technology does and give you a way to verify it, rather than relying on badges.

For the formal details, read the privacy policy and the terms of use.