Browser extension that adds customizable dark mode support for PDF files to reduce eye strain while reading.
This project is licensed under the GNU General Public License v3.0 (GPL-3.0).
See the LICENSE file for details.
This project was originally inspired by and partially derived from:
- DarkPDF by ArshSB
https://github.com/ArshSB/DarkPDF
DarkPDF is licensed under GPL-3.0, and this project complies with the terms of that license.
All modifications, additional features, UI changes, entitlement logic, and ongoing maintenance in this repository are independently developed for PDF Dark Mode.
I had to read a bunch of PDFs at night during exams. Black text on a white background caused significant eye strain, and existing extensions did not provide enough customization for readability and comfort. PDF Dark Mode was built to solve that problem with adjustable reading controls and additional viewing modes.
- Supports both online and offline PDFs
- Toggle dark mode
- Adjustable darkness strength
- Adjustable contrast
- Core PDF dark reading experience
- Additional reading modes:
- Sepia
- AMOLED
- Per-site allow/block rules
- Per-site overlay area presets
- Lemon Squeezy license key activation and validation
- Future premium productivity and customization features
Pro is a one-time purchase. There is no subscription and no renewal, and a purchased license covers Pro features added in later versions.
- Pro access is activated using a Lemon Squeezy license key.
- License status is validated automatically in the background (no manual validate step in popup).
- Validation is throttled to periodic checks (about every 24 hours), not on every popup open.
- Stale-while-revalidate behavior is used: if a previously active license is stored locally, Pro remains available while background validation runs.
- If Lemon Squeezy reports the license as invalid or inactive (for example after a refund or chargeback), Pro access is removed on the next successful validation.
- Network failures never revoke Pro. Access is only withdrawn when Lemon Squeezy explicitly rejects the key.
PDF Dark Mode does not collect or transmit personal browsing data.
Current analytics functionality is:
- local-only
- stored on-device
- not sent to external servers
The extension makes exactly one network request, and only when you activate or
revalidate a license: api.lemonsqueezy.com. There are no analytics endpoints,
no CDNs and no webfonts — everything the UI needs is bundled, so the popup and
the instruction pages work offline and leak nothing to third parties.
- Website: https://pdf-dark.com/
- Chrome Web Store: https://chromewebstore.google.com/detail/pdf-dark-mode/clabimobhdkbfpkdeloigeneocldkmdc
- Microsoft Edge Add-ons: https://microsoftedge.microsoft.com/addons/detail/pdf-dark-mode/nghkmkbjhpgdibgopgekgjnbocfmnjdo
- Help: https://pdf-dark.com/help.html
- Email: contact@pdf-dark.com
No build step and no dependencies — load the folder as an unpacked extension via
chrome://extensions with Developer Mode on.
node tests/run.js
The suites are plain Node, no framework:
| Suite | Guards |
|---|---|
overlay-parity |
The overlay CSS still matches the pre-refactor output, across 1080 input combinations |
visibility |
The truth table for when the overlay is shown, including the global on/off switch |
policy |
Which URLs count as PDFs, including the false positives that used to darken search results |
content-smoke |
invert.js runs against a DOM and actually paints: overlay, dock, sepia, re-injection |
popup-smoke |
popup.js runs against the real popup.html element set, for free and Pro |
worker-smoke |
Injection, the keyboard shortcut, cross-tab syncing and first-run defaults |
integrity |
Manifest references resolve, scripts parse, no third-party requests, no duplicated overlay code |
The suites above are fast but they stub Chrome. Some failures only appear in a real browser, so there is an end-to-end test that loads the extension unpacked, opens real PDFs and inspects the live DOM:
CHROME_BIN=/path/to/chrome node tests/browser/extension.test.js
It skips cleanly when no Chrome binary is present. It covers first-load darkening, the floating dock, live toggling in an already-open tab, upgrading from a 2.1.3 profile, and the popup rendering — and it reports any error thrown inside the service worker.
Run it before publishing. The stubbed suites once passed while the extension
was visibly broken: a hasPdfEmbed() check looked for
embed[type="application/pdf"], which Chrome never exposes for a top-level PDF,
so dark mode silently stopped applying. Only a real browser caught it.
scripts/core.js is the single source of truth for two decisions: whether a page
should be darkened, and what the overlay looks like. It is loaded by the service
worker (importScripts), the content script (injected ahead of invert.js) and
the popup (<script>).
That logic previously existed as three hand-maintained copies which had already
drifted — the content script recognised Google Drive URLs the worker never
injected on, so the code was unreachable. If you change the rendering maths,
change it in core.js and let overlay-parity tell you what moved.
core.isDefinitePdfUrl() only trusts the pathname, because testing the whole
URL for .pdf darkened any page that merely mentioned one (searching Google for
report.pdf turned the results page dark).
Everything else that mentions a PDF is ambiguous: the script is injected, but
core.isPdfDocument() has to confirm it before anything is painted. That check
reads document.contentType first — Chrome renders a top-level PDF in a separate
plugin process, so the content script sees an empty body and no <embed> at
all. Element matching alone is not enough, and relying on it broke every
?file=x.pdf style endpoint. The element selectors remain for PDFs embedded in
HTML pages and for pdf.js, which paints into <canvas>.
Contributions, bug reports, and feature suggestions are welcome.
Please open an issue or submit a pull request if you would like to contribute.
Commercial distribution and paid feature offerings are permitted under GPL-3.0, provided that GPL obligations and license terms are respected.
- Updates will continue gradually
- Additional accessibility and reading features are planned
PDF Dark Mode is an independent project and is not affiliated with or endorsed by the original DarkPDF project or its contributors.