I am thinking of buying the imperial edition on sale right now. I don't see the manual listed in the description. Is it included in the actual game after installation? Is there a build in players manual integrated into the game? I need a fast response before the sale is over...
Thanks

No

One of the best manual source is from https://www.d20pfsrd.com/
Its from the table top game but almost everything is the same.

This is a good source for rules: [url=https://pathfinderkingmaker.gamepedia.com/Pathfinder:_Kingmaker_Wiki]https://pathfinderkingmaker.gamepedia.com/Pathfinder:_Kingmaker_Wiki[/url]

There is no official manual, which is a little frustrating considering the game has pretty complicated mechanics. If it is your first playthrough, play with the tutorials on until you get the hang of things.

Edit: you'll have to copy/paste the URL, as the GoG forums are giving me problems with links.

considering it's roughly 100h game the price tag is pretty low and the game is constantly on one sale or another as of late to boot. If they added tutorials it's be a whole load of text. They'd pretty much had to port php in entirety and just a text dump would not please anyone either so it'd cost a lot of money that went into content instead. And there is an advantage in having pnp as your system as you actually can skip those things and assume people read the phb.
Same with mod support. It was pretty much either developing mod tools or making a bigger game.