Eventually Mohammad had all the idols burned.
To Moslems that is very important. To Westerners, and to more than one Turkish sultan, it was much more important to know that acient texts were buried in the earth, and in caves near Mecca.
Mohammad himself said he was in a cave in the area and reached down to pick up a text to read (allegedly at the command of an angel.)
Forget about the angel for a moment, we have Mohammad's own testimony that there were texts in a cave to read. Whether he or a close confederate read them, Mohammad recited the words to other people.
None of this is difficult to believe, and we do, in fact, have the testimony of hundreds of people concerning how Mohammad recited Holy Writ.
Jews and pre-Judaic Hebrews had followed the trade routes that run through Arabia for centuries. Abraham himself followed those routes. As far as I have learned anything about the matter it has always been the custom of the Jews to bury a worn-out Torah in the earth, the same as the Jews bury their dead in the earth.
The probability of having a Torah buried in and around Mecca is very good. The probability of having even more ancient Hebraic texts buried there is also very good, and we might even be able to find buried texts containing the disposition of property owned by various persons found in the Bible.
Mohammad said changes had been made in the texts attriuted to God. He could say that if and only if he had more than one copy, At the same time he seems to have never obtained a full copy of any of the Gospels or the Letters.
On the other hand, Mohammad probably had more and better access to ancient documents than anyone else in the world at that time since this was the worst part of the Dark Ages. No doubt he made mistakes. No doubt there was no one around to correct them!
Because of the discovery of the Dead Sea Scrolls, we know that, around the time of Jesus (600 years before Mohammed), the Torah was pretty much the same as it is today. If any ancient pre-Torah texts were found buried in Arabia, they would have been written in an ancient Phoenician script which no Jew or Arab of his time would have been able to read. Since about 1000 years before the time of Mohammed, the Jews had changed over from Phoenician script to the square Assyrian script in which all modern Torahs are written.
So, the idea that Mohammed based the Koran on some ancient Hebrew writings is highly unlikely.
If Bill Clinton is any example, Muhammad, or indeed any person, could also say that if he just made it up off the top of his head. Which he may have had to- how many languages could he read, even if he had found manuscripts?