Quran is the greatest miracle in the whole history of the world, which proves that it can never be made by any one but Allah with His unlimited powers and unlimited Knowledge.
Miracle is something that people can not do it e.g. Prophet Jesus was granted by Allah the ability to revive the dead and cure the cureless. His miracles were limited to his time and no one can witness any of Jesus miracles now. The miracles of Quran is everlasting and can be witnessed by any one, any where and any time. Quran has challenged its enemies who used to claim that it was made by Muhammad, to bring like Quran even if the gather all their allies and supporters from Jinns and humans. The enemies of Quran failed to stand to the challenge. Allah then challenged them to bring ten chapters like the chapters of Quran which are 114 chapters. They failed again. Then Allah challenged them to bring just one chapter like any of the 114 chapters of Quran. They failed again. This challenge has proven that Quran is never from any human source otherwise the enemies of Quran could have brought anything like it even one chapter like any of its 114 chapters. Millions of Arabs today are non Muslims and they know the Arabic language very well, yet none of them could make even one line like Quran. This is an evidence which is enough for any one who thinks in proper way.
Quran was revealed on the Prophet Muhammad (SAWA) from Allah (SWT) and the allegation of obtaining it from Christians and Jewish communities has no scientific value at all, when you read Quran and compare it with the Jewish and Christian texts. Some similarities are there because the common origin of all the three texts is from Allah, but Torah and Bible were distorted while Quran remained remained constant and unchanged.