Eclipse Community

https://addons-legacy.palemoon.org/addon/pdf-js-for-seamonkey/

Addons like Dark Background And Light Text used to be able to also works on PDFs. The Swarth fork of Dark Background And Light Text doesn't work on PDFs anymore.

https://addons-legacy.palemoon.org/addon/swarth/

On Firefox, there is this trick to do so:

https://pncnmnp.github.io/blogs/firefox-dark-mode.html

Does this trick work with Pale Moon PDF reader addon, too?

I think it's better to consult the Pale Moon experts first. They banned me on their forum so I can only ask here.

I confirmed this trick works on LibreWolf.