The entire Islamic world believes that the Quran is infallible. This belief is so rooted in their psyche that when a Muslim friend of mine introduced me to Islam, he presented this as evidence of the divine origin of the Quran. He argued that because the Quran unlike all other holy books has not been changed it must be from God.
Whether the Quran is infallible or whether it has been corrupted or not are two different subjects.
As for the first question the answer is that the Quran is not infallible. It contains thousands of errors, absurdities, contradictions, inaccuracies and sheer nonsense. It contradicts logic, history, science, the Bible and even itself. It even contains grammatical errors that show its author was an illiterate man. Hardly can you find a book as absurd as this book. It is so poorly written that I cannot call it literature.
As for the other question, we don’t know. The Quran we have is the one compiled by Othman. He burned all other versions of the Quran so there can be no disagreement among Muslims. It is clear that the other versions must have been different from the one chosen by him otherwise he would not have burned them. How did he determine his version is the correct one and the other versions are not? There was no way for him to know for certainty. It is very possible that his pick was not the right one. However, since all other versions are destroyed, it is impossible to say whether the one we have is the authentic one.
Just see what has happened to the hadiths. Various people have reported the same story is various ways. They defer in details. The verses of the Quran could have also suffered similar fate, although perhaps not to that extent, because they were memorized.
However, with a little rational thinking, we can assume since Othman had to burn the other versions to avoid discrepancy, this book must have been altered. It is also possible that many of the verses of the present Quran are not what Muhammad said. The original verses may have been the ones that were burned. Many verses may have been lost forever. It is also possible that some verses have been added to the Quran that were not originally said by Muhammad.
===================================================================
2:106 We do not abolish a verse unless we provide a better verse.
Contradiction: 10:64 There is no change in the words of Allah.
=============================================================
The Quran is well preserved ?
It was narrated that ‘Aishah said: “The Verse of stoning and of breastfeeding an adult ten times was revealed, and the paper was with me under my pillow. When the Messenger of Allah died, we were preoccupied with his death, and a tame sheep came in and ate it.” Sunan Ibn Majah1944