[Jedd]

Yeah, it's well hidden - I'm sure I've looked for okular support for mobi & epub a while back, mostly because 'ebook-reader' that comes with calibre is a bit pants.

Must have been quite a while back, I guess.

On Debian unstable I'm seeing okular-extra-backends (as mentioned) along with packages for ODP and ODT, as well as an okular-mobile package (postscript, dejavu, DVI, comic books, fictionbook, Plucker, etc.

I've just tried this with an Asterix comic in .cbr format - no joy.

Works a treat with a Deadpool .cbz file though.

For CHM, and I've not [ found / been forced to acquire for want of a better format ] any of those since 2008, kchmviewer is pretty fine (I'm a KDE user so it fits nicely, though like most KDE apps it only wants some KDE / QT libraries to run on your preferred DE).