simplerthan

How it works

Short version: your browser opens the file, a program inside this page does the work, and you download the result. This site has no way to receive a file.

What happens to a file

  1. You choose a file. The browser lets this page read it. Nothing has left your device yet.
  2. The page hands the bytes to a worker running in your browser. The worker uses open source programs compiled to WebAssembly: qpdf to rearrange pages, mozjpeg to recompress pictures, and pdf.js to draw page previews.
  3. The result is built in memory and offered as a download. When you close the tab, it is gone.

Check it yourself

  • Watch the network. Open your browser's developer tools (F12), choose the Network tab, then add a file and run a tool. You will see requests for this site's own program files the first time, and none that carry your file.
  • Go offline. After the page has loaded, turn off Wi-Fi and use a tool. It still works. A tool that needed a server could not.
  • Read the meter. The panel at the bottom of every page lists what the page loaded and flags any request that carries data or goes to another site. It can only see requests made by this page's own scripts, so treat it as a convenience and the first two checks as the proof.
  • Read the policy. The page's Content Security Policy tells the browser to refuse connections to anywhere but this site. The browser enforces that, not us.

What we do see

Cloudflare delivers this site. Like any web host, it records ordinary access logs: the address of the visitor, the pages and files requested, and the time. We add no analytics, cookies or tracking scripts of our own. The file names and contents you work with are never part of those requests.

Limits worth knowing

  • Size. Up to 500 MB per file. Very large files may run out of memory, especially on phones. If that happens you will see a message, not a crash.
  • Locked files. A PDF with an open password asks for it. A PDF whose author forbade editing or combining is refused unless you enter the owner password. We do not strip protection.
  • Signatures. Any change to a signed PDF breaks its digital signature. We warn you first.
  • Merging. Bookmarks and form fields from the first file are kept; files after it lose theirs.
  • Compressing. We recompress pictures and tidy the file. We never turn pages into pictures. Text-only files barely shrink, and when a file cannot get smaller you get the original back.
  • No guarantee. Check the result before you rely on it, and keep your original.

What is inside

Programs used in your browser, with their licences in licenses.txt: qpdf (Apache-2.0), mozjpeg through jSquash (Apache-2.0 and BSD-style), and pdf.js (Apache-2.0). The engine that connects them is ours.

This page was built from engine …. The code that runs in your browser is listed with checksums in engine.json.