iBook crashes with big PDFs

Why iBooks closes unexpectedly when I open a large pdf it’s really frustrating and upsetting because because when I open iPad to study then it starts crashing. Huge number of people already complained about this thing but still Apple did nothing for this problem,just because of this problem am going to buy new iPad and I heard those iPad also have same issue and people are suggesting if you are student don’t buy Apple iPad , we students are really having big problem because of this issue please Apple help us, and give us some solutions.