Fact: DotA can't load in your World Editor? Read how they edit DotA!

Firstly, if you want to edit DotA maps, you can't expect to edit them like you edit maps in World Editor.
Icefrog and other DotA maps editors (OMG mode, Fun, AI...etc) edit the maps by using an .MPQ viewer (<<I don't quite remember the name... Read here!)
They edit it using the JASS computer language. They opened (more like decoded) the map into codes and edit it. So it is not quite easy for beginners since you still need to understand how the code works. It is extremely tedious. There is about 26000 lines and 1000+codes there. And do remember that every skill in DotA is marked with slightly different numbers and words such as A2O4 or A4C2 ( << just randomly mentioned them for a real example, check out the changelog for DotA. If there is new ability, there is a button to show the code. And after you clicked it, it will show "Ability code : ...." the dots are for the random words and numbers)
So, if you still want to edit it, please click on the link above or this link, they are the same...