Everytime a revelation was sent to Mohammad(pbuh), his companions would write it down on whatever was available and sometimes they would memorize it. Prophet Mohammad(pbuh) would also memorize and he would check what his companions has written down by asking one of them to read it for him, and he would hear those who had memorized to also, this way it would be authorized. He would clear any mistakes his companions made. In this way the Quran was written down under Mohammad(Pbuh) supervision. Even the order of the verse revealed to Mohammad(pbuh) was completed under Mohammad(Pbuh) supervision. Every Ramadan, the verses that was revealed to Mohammad(Pbuh) were recited and on Mohammad(pbuh) last Ramadan, it was rechecked and reconfirmed two times. So it is very clear that the Quran was compiled and authenticated by prophet Mohammad(pbuh) during his lifetime. When Abu Bakr(the first Caliph) became the caliphate, he compiled the Quran in one common material and tied it with strings so that no part of the Quran was lost.
Many companions of Mohammad(pbuh) wrote down their own version of Allahs revelation to Mohammad(pbuh) and not all of them were authenticated by Mohammad(pbuh). hence a dispute among Muslims began over the different contents of the Quran, this dispute began during the reign of Caliphate Usman(r.a). consequently Usman(r.a) borrowed the copy of the Quran which was authenticated by Mohammad(pbuh) and put in one common material by Abu Bakr(r.a) from Hafsha(r.a), Mohammad(pbuh) wife. Usman(r.a) ordered four companions who were among the scribes to make copies of the authenticated Quran, Usman(r.a) burned all the copies of the Quran which didnt match the Original one. two of the authenticated Qurans that were copied by Usman(r.a) are still available, one Tashkent in erstwhile Soviet Union, the other in Topkapi Museum in Istanbul, Turkey.
The original Quran does not contain the signs indicating the vowels in Arabic script, because the Arabs were in not in need of them, sinc Arabic was their mother tongue. The signs were put in for Non-Arabic people so they can pronounce the words right.
Allah has promised in the Qur’an :
"We have, without doubt, sent down the Message; and We will assuredly Guard it (from corruption). [Al-Qur’an 15:9]
I know that Mohammad(pbuh) could not have read the Jews and Christians scriptures and copy it, since Mohammad(pbuh) was illiterate. Sura 4 being parrallel with the infancy gospel of james doesnt necessarily mean that sura 4 was plagarised, it could go both ways, it could mean that sura 4 is of divine origin and is confirming the old scriptures(which i believe) or it could mean it was plagarised, sura 4 being same as the infancy gospel of james could mean of the above statements, not just one of them.
The pharoah of exodus is not known with 100% accuracy, some say, Thutmose III, some say Ramses II, some say Merneptah, Horemheb, etc. But the true pharoah in my opinion is the one described in the Quran. And according to most scholars, the city of Ramesses was built by Ramsses the II. the city of Rameses, named Pi-Ramesses or Per-Ramesses, meaning "house or domain of Ramsesses". Now this would put the date of exodus some time after 1313 B.C. so how can Thutmose III be the pharoah at a time when the city of Ramsesses was already built.
there are lots of theories.
thank you.