Dark mode PDFs in Chrome
Chrome has no dark mode for PDFs. Its dark theme covers the browser, extensions cannot reach the viewer, and the experimental flag that does reach it makes a mess of images. Converting the file avoids all three.
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Why extensions stop at the PDF
A dark mode extension works by rewriting a page's styling, so it needs a web page to rewrite. Chrome does not display a PDF as a web page \u2014 it hands the file to a built-in viewer that draws it directly. There is no styling for the extension to alter, which is why an extension that darkens the entire internet stops dead at a PDF.
The force-dark flag reaches it, and that is the problem
Chrome has an experimental setting, Auto Dark Mode for Web Contents, that will affect a PDF. It was built for websites without a dark theme of their own and knows nothing about document structure, so it works on rendered pixels: photographs invert, diagrams become hard to read, and colours come out odd. It also applies browser-wide, to everything you look at, and it is experimental for a reason.
Screen filters darken the wrong thing
Whole-screen tinting and inversion tools do reach the PDF, because they sit in front of everything. That is also their flaw: they dim your entire display, invert photographs along with text, and switch off the moment you stop reading. The file is unchanged, so it is white again on your phone and white again when you print it.
Changing the file instead
Converting produces a normal PDF that is dark in Chrome's viewer, in Firefox, in Acrobat, on a phone, and offline. No extension, no flag, no filter, and no side effects on anything else you are looking at. Photographs keep their own colours and charts keep the colours their legend refers to.
Still a normal document
Text stays selectable and searchable, so browser find still works, links inside the document keep working, and you can print it or pass it on without it reverting to white.
Questions
Why does my dark mode extension not work on PDFs in Chrome?
Because extensions restyle web pages, and Chrome renders PDFs in a built-in viewer rather than as a web page. There is no styling to rewrite, so the extension has nothing to act on.
Does Chrome have a built-in dark mode for PDFs?
No. Chrome's dark theme covers its own interface, and the PDF keeps the colours stored inside the file.
What about the Auto Dark Mode flag?
It will affect a PDF, but it was designed for websites and works on rendered pixels, so photographs invert and diagrams become hard to read. It is experimental and applies to everything you browse, not just the document.
Will the converted file still be searchable in the browser?
Yes. Text stays selectable and searchable, so browser find still works, and links inside the document keep working too.