There’s a lot of crap out there in google land when you try and search for a offline version of drupal’s documentation. I’ve been searching for this for quite some time and never came across the final bullet proof solution for offline drupal documentation.
You basically have to use the API module and set up a local drupal site to create and serve the documentation, somewhat cumbersome, but as far as I can tell there is no better way right now. Full instructions are here: