I am sure because God is in this Word. Reading it and seeing it fit from Genesis, through Revelation, shows me that only God could have authored this book.
Also, since satan has fought this version, or translation more than any other, and still fights it today, proves it is of God.
I find no fault with it. I find no error in it. Instead I find glory, blessing, comfort and leadership in these heavenly words. Only the true God could give such live words.
Jo