I've just re bought this game via GOG, it said it would come with the DK2 Editor, I cant find it anywhere in the files, is anyone able to shed some light as to where it might be?

You can download all editors from lubiki: https://lubiki.keeperklan.com/html/dk2_tools_mapedit.php

I've downloaded the Editor but when I put it in the correct place within the DK2 file it opens then closes straight away, not allowing me to make maps or anything, any ideas?

Sorry, I don't, it should just work out of the box. Are you sure you installed it right?

I fixed it :) any idea how to make Hero Portals work with custom maps, as i cant seem to get them working :/

Please share for future readers what your problem was and how you fixed it.

But all this stuff comes straight from the Keeperklan DK2 mapmaking forum.

See this topic for a full explanation: https://keeperklan.com/threads/642-Creating-maps-with-HERO-PORTALS

Log into GOG and go to your games
Then under DK2 where it gives you the option to download galaxy or the offline installer, look right of it
You'll see "extras", under there it has the dk2editor under the reference card and manual.
I bought this years ago (recently decided to reinstall) but its always been there