Dark mode PDFs on a Mac
Turning on macOS dark mode darkens Preview around the page, and leaves the page itself glowing. Convert the file and it is dark in Preview, in Safari, on your iPhone, and when you send it to someone.
No account required. Preview free, then £0.99 per document.
What macOS dark mode actually covers
System dark mode restyles the things macOS draws: menus, window chrome, sidebars, Preview's toolbar. A PDF is content being displayed inside that window, with colours of its own, so it is left alone. This is consistent rather than broken — the same reason a photograph does not change colour when you switch appearance.
The accessibility route, and why it is not the answer
System Settings → Accessibility → Display offers Invert Colours, which will certainly darken the page. It also inverts everything else on the screen at the same time, turns every photograph into a negative, and stays on until you switch it off. It is a genuine accessibility tool and a poor reading setting.
Why Preview will not save a dark copy
Even where a viewer can show you a document with altered colours, it will not write those colours back into the file. Export the PDF, AirDrop it to your iPad, or print it, and it is white again — because nothing about the document ever changed. Only editing the file makes the change travel with it.
One file, every Apple device
Converting produces an ordinary PDF, so it is dark in Preview, dark in Safari, dark in the Files app on an iPhone, and dark in whatever your colleague opens it with. Text stays selectable, Spotlight can still find it by its contents, and Quick Look shows it correctly.
Questions
Why does dark mode on my Mac not darken PDFs?
Because dark mode restyles what macOS draws — menus, toolbars and window chrome — while a PDF is content with its own colours stored inside it. Changing the page means changing the file.
Is Invert Colours in Accessibility a good workaround?
It darkens the page, but it inverts the whole screen, turns photographs into negatives, and only applies while it is switched on. It is designed as an accessibility tool rather than a reading mode.
Can Preview export a dark version?
No. Viewers can display altered colours but do not write them into the PDF, which is why the file is white again on another device. Converting the file is what makes the change permanent.
Will it still work on my iPhone and iPad?
Yes. The result is a normal PDF with different colours, so it opens dark in Files, Books, Safari and any other reader, with no app or setting required.