King David c. 1040–970 BCE, indeed any of the ancient Jewish kings, if presented with a modern Sefer Torah would not have been able to read it. The masoretic text we now have, written between the 7th and 10th centuries CE (see: wikipedia), uses an entirely different alphabet -- with, using round numbers 1,400 years between them.
The accepted answer here (currently approved by 13 people) states "There are various proofs that the Torah we have is essentially identical to the original (with some minor spelling variants)." But there appears to be demonstrable evidence of "change" in the alphabet, which would strongly indicate the probability of (potentially significant) change to the text itself.
Why then, does Orthodoxy hold that the Torah has not changed?