How to read PDFs in dark mode

A PDF carries its own page colours, so switching your app or phone to dark mode usually darkens only the menus around a still-white page. You have two ways round it: tell your viewer or device to invert colours on screen, which leaves the file untouched, or make a dark copy of the PDF itself, which looks dark in any viewer but turns each page into an image. The PDF dark mode tool I built does the second, on your device, and this guide covers both.

Why PDFs stay white

A web page is flexible: it can check whether you prefer a dark theme and restyle itself. A PDF is a fixed description of a printed page, with every letter, line and colour placed exactly, and it has no idea what theme your device uses. That fixed layout is the whole point of PDF, as How PDF files work: why some have text and some are pictures explains, and it is why a viewer's dark mode usually stops at the toolbar.

Option 1: your viewer or device

The least destructive approach is changing how the page is displayed. Some PDF readers can recolour pages; Adobe Acrobat Reader, for instance, has an accessibility setting to replace document colours, and many mobile and e-reader apps have a night or inverted mode. If yours does not, the operating system can invert the whole screen: iPhone and iPad have Smart Invert and Classic Invert in the accessibility display settings, Android has colour inversion, and macOS and Windows have similar options. The file stays exactly as it was, text remains selectable and searchable, and you can switch back in a second. The downside is that inversion is blunt: photos turn into negatives, and a system-wide setting affects everything else on the screen too.

Option 2: a dark copy of the file

When you want a file that is dark wherever you open it, on an e-reader, a tablet or a laptop, the dark mode tool makes one. It renders every page at the resolution you choose (120, 150 or 200 dpi), flips light and dark so the background goes dark and the text light, and maps the result onto one of three themes: a soft dark grey with light grey text, pure black, which saves power on OLED screens, or a warm night sepia. With the keep-colours option on, it rotates the hues back after inverting, so red stays red and photos look like dimmed photos rather than negatives. The pages are then rebuilt into a new PDF at the same page sizes. Everything happens in your browser, and the document is never uploaded.

What a dark copy gives up

Because each page becomes a picture, the dark copy loses everything that made it more than a picture:

• Text can no longer be selected, searched or copied, and screen readers cannot read it.
• Links, bookmarks and form fields do not carry over.
• File size often grows, especially for text-only documents, because compact text becomes images; the PDF compressor can shrink it again.
• Colourful pages, photos and complex charts look less natural than plain text.
• Printing it would use a lot of ink. It is meant for screens.

So keep the original. Read the dark copy, and go back to the original when you need to search or quote it; the PDF text extractor pulls the text out of the original if you want it separately. If what you actually need is a black-and-white copy for printing, the PDF grayscale tool is the right one.

Comfort tips for night reading

Dark pages help most in a dim room, where a bright white page is glaring. In daylight, dark text on a light background is often easier to read, and research on whether light-on-dark text is better overall is mixed, so use whichever feels comfortable rather than treating dark mode as automatically better. Many people find light grey on dark grey easier than pure white on pure black, which can seem to glow or smear for some readers, which is why the soft grey theme is the default. Turn the screen brightness down rather than relying on the theme alone, enlarge the text instead of squinting, and look away from the screen regularly on long reading sessions.