Fact of the matter is this.
As kiwi chick has stated, Airservices receives a LOT of applications for ATC. It's one of the few places you can receive fre... paid training for a highly remunerated, professional career. The people who are accepted on the courses may be indivduals, but every single one of them is one thing at least. Smart.
As any one of these current or ex smart trainees will tell you, the ATC course is hard. It's like no other job you've ever done, regardless of your external experience. To pass, you are going to need enough motivation to really, really want the job, and even then it might not be enough.
Pre-course reading? No one is going to check whether you have done it. All I can say is that if I really, really wanted the job, I'd reckon I'd have the motivation to digest every bit of it out of sheer interest.
Besides, who knows, considering that trainees have been 'invited not to attend' after failing only 2 theory exams in the past, and more importantly that the lack of theoretical understanding is the undoing of a large number of trainees who crash out of the simulator, it might even make the difference between passing that very hard course and failing it.
But I digress.
No, you don't 'have' to*
* The, on average, 5 or 6 trainees out of each course of 12 who 'pursue different options' may disagree with that advice