About PDF Dark

PDF Dark is a free, browser-side tool for reading PDFs in dark mode.

It started as personal frustration — reading long PDFs at night meant either staring at a white page or uploading the file to a service whose privacy I didn't fully trust. Neither was great. The “invert colors” options on existing tools also mangled photos and charts, turning graphs into noise and faces into X-rays.

So PDF Dark was built around two non-negotiable defaults:

• Nothing leaves your browser. The file never touches a server — you can confirm it yourself in DevTools → Network.
• Images keep their original colors. A saturation-based algorithm detects photos and figures and leaves them untouched while it darkens the rest.

Everything else — the four themes, the downloadable dark PDF, the iOS Safari support — grew out of those two defaults.

Who runs this

PDF Dark is built and maintained by an independent developer, not a company. There's no team, no investor, no upsell. If you spot a bug, need a new feature, or just want to say hi, email hello@pdfdark.org.

How it works under the hood

• PDF rendering: Mozilla's PDF.js — the same open-source library Firefox uses
• Dark-mode algorithm: pixel saturation classification, runs in a Web Worker so the UI never blocks
• PDF assembly: pdf-lib, to stitch themed pages back into a downloadable file
• Hosting: Vercel
• Error monitoring: Sentry, activated only when something actually breaks — with all content masked so the replay never captures your PDF

Why it's free

Right now, nothing — PDF Dark runs on free-tier hosting and costs me very little to keep online. If usage grows enough that it stops being free, the most likely next step is a small, unobtrusive ad on the landing page (never inside the PDF viewer). There will never be a paywall on the conversion itself.