The Quran came down through recitation from Gabriel to Mohamed (S) and not book form, as this question has come before from non-believers like yourself through the centuries and Allah has mentioned this in surah Al-Ancam ayah 7
7. And even if We had sent down unto you (O Muhammad) a Message written on paper so that they could touch it with their hands, the disbelievers would have said: "This is nothing but obvious magic!"