The full official game file.Version V1.0. Working with 1.6.2 update.
How to download the mod :
Create a folder called "mod" in your Heart of Iron IV directory.
Then download the Great Serbian War V1.0 and take the files inside the rar. file
and then put them in you're Hearts of Iron IV "mod" folder.
Then just start up the game and everything should work perfectly. ;)