Anything, that comes close to a manual is the glossary ingame. I searched the web and found something called "PDF Adventure Manual", but apparently that was for kickstarter pledgers only.
I really need a PDF, because I wanna put it on a tablet/reader and read it offline.
The game is complex enough that the devs should at least have provided a manual (electronically). It's a shame they didn't... I would even pay for the this manual if it was for a "special edition" here on gog...

what are you finding complex exactly?

Okay let's make it quick: if this is, where you tell me how much of a noob I must be to find this game complex, spare me. I'll stop you right there ;)

If it was an honest question: there is a certain amount of different characters of which you can form different parties. Each character has stats and skills and I'd like to read, how the different skills affect the different stats of the enemies. I would like to read everything that's in the glossary outside the game.
I don't think, the game is more complex, than any other RPG that brings a certain game mechanics.
But it's a lot more complex than an arcade racer or a football game or a point and click adventure, with this said, I hope we are on the same page...

The single most useful resource for this game is the curio interaction list You can find here:
http://darkestdungeon.gamepedia.com/Curio

This wiki has all the other information You might want as well and seeing as it is linked to by the developers site, I assume it's somewhat offical.

I'm like You and like to be offline so I downloaded the curio page and just browse it offline when necessary. The web is rife with instructions on how to save webpages for offline use for android as well so I won't link any of those.

Didn't think of that, good idea. I'll give this a try :) thx

Still think it would be great to have a pdf for my eBook reader :)

EDIT: I might have found, what's working for me: printing the wiki pages with pdf creator ;) ... it's not so easy on the eyes with lots of blank space. But I guess it'll do :)

Yes, I thought that was a shame too! The wikipedia has comprehensive information though. It's not always up to date as to numbers but it explains mechanics well. Still, it could be a nice idea to write a manual!