In fact, there are good reasons to believe that the Bible has not changed in any significant way from its original form.
God began the process of revealing His Word by giving Moses the Ten Commandments, written in stone by His hand. For people to know what God wanted, and know that it hadn’t changed, it had to be written down. The first five books of the Bible, known as the Book of the Law or the Pentateuch, are also called the Books of Moses (because he was largely responsible for writing and compiling them). These foundation books were kept in the Tabernacle and the priests were to teach the people of Israel from them, reading them aloud to the people every seven years during a special celebration. Various other books in the Bible mention being recorded in writing and it is likely that by 300 BC, the Old Testament books had been collected and were recognized as the words of God.
Although there are no remaining original bible manuscripts of the Old Testament, the scrolls were carefully copied when the older ones wore out by the Jewish people. In fact, the Scribes, whose job it was to copy and preserve the texts, had very strict rules to follow. For example, they could not write words from memory, and if they made more than three mistakes on a page, they had to destroy it and start again. There are around 3000 Hebrew manuscripts of the Old Testament, and several thousand more manuscripts of translations of the Hebrew Old Testament. The oldest complete manuscript of the Hebrew Bible has been dated to around 1008 AD, and the Dead Sea Scrolls (which did not contain the complete Old Testament, but at least fragments from many of the individual books) discovered in 1947 are dated from 250 BC to 135 AD. Scholars have compared the texts available and found only a small number of differences and of those, a very small portion that make any significant difference. Most modern translations make note of these differences where they occur and because of this, the Old Testament that we hold in our hands today, is a document that can be considered completely trustworthy.
The New Testament, having been written later, has manuscript evidence much closer to the original copies, ninety-nine having been produced before 400 AD! In fact, out of all the writings from antiquity, it is the best attested set of writings. Early on it was translated into a variety of languages and there are between 20,000 to 25,000 handwritten copies of the New Testament in various languages. Due to the overwhelming number of manuscripts available, there are consequently also an abundance of textual differences. However, most of these are spelling and nonsense errors, minor changes such as using “the” or not, or where it is obvious from the majority of other texts to be an error. Only a very small number of differences actually change the meaning of the text. However, these are noted in modern English translations and it is unlikely that we are missing any significant reading.It is reasonable to conclude that the Bible we have today can be counted on to be an accurate representation of the original.