When thinking about the authenticity of scriptures, we have to go back and look at how they were written. The Bible was a compilation of writings by many people. It was preserved through great sacrifice on the part of many people. I think most Bible scholars will admit that some of the original texts were lost in translation, or purposefully omitted. (To learn more about some of the books of the Bible that were lost, click this link.) I would like to be able to say that most Christians believe it is God's word, despite the changes that have occurred. But frankly, today many Christians pick and choose which parts they will believe. Some believe the New Testament, but not the Old. Some believe the account of the Savior's ministry, but not the account of the creation. There seem to be two different sides in this argument; namely the side that believes the Bible is word perfect because God intended for the writers to write every word in it the way we have it today, and those who believe that although it may not be word perfect, it still contains God's word. My feelings about it's origins, and the way it has been preserved for today, fall somewhere in between.
I do believe that the Bible is the word of God. I prefer to use the King James version because as I have read other popular modern translations, I feel sometimes that certain nuances are lost. I also believe, as stated in the Book of Mormon, that many "plain and precious parts" were lost during the years following the Savior's death, so I don't necessarily believe it can be considered "word perfect".
Joseph Smith attempted to retranslate the Bible, but was unable to finish the task before his death. But in many cases, his translation adds greater understanding to the scriptures he translated. You can read his corrections by clicking this link.
Our church website goes in to some detail about our view of the "canon" of the church. Included in this explanation is a partial recount of how the Bible came to be. You can read this by clicking this link.
But when deciding if a book of scripture such as 2 Peter was, or was not written by the purported author, I feel the best test is to determine if the writing follows the gospel of Jesus Christ. In addition, we can seek inspiration from God to know if that text is His word.
What I find most interesting about this whole discussion is that there are many Christians who believe the Bible, despite it's unknown origins, yet will not accept the Book of Mormon, of whose origins we are quite clear. Most Christian scholars will carefully study the works of Greek and Roman philosophers, who were not actual apostles or prophets of God, but won't accept the Book of Mormon which we believe was written by servants of God, under the inspiration of the Holy Ghost.
Some might say that they don't believe Joseph Smith was a prophet, and that he didn't receive the Book of Mormon in the way he reported. Would God would not work in this way? Would God allow the Bible to go through many centuries of change, but still stand as His word, but not bring forth scripture in any other way? We believe it is precisely because of the loss of scripture, and the changes that have occurred that God preserved the Book of Mormon to come forth in purity in the latter days so that it could be a second, pure witness of the Savior Jesus Christ. The Book of Mormon restores some of the lost "precious parts" of the original writings of the Bible.
Those who cannot accept that an angel appeared to Joseph Smith, and revealed the location of the Book of Mormon, surely must have trouble believing that Moses parted the Red Sea. Those who cannot accept that Joseph Smith translated the Book of Mormon by the gift and power of God, surely cannot accept modern miracles. To quote a popular Christmas song, "God is not dead, nor doth He sleep." Was the Bible enough scripture for all time? We believe "In the of or witnesses shall every word be established." 2 Cor. 13:1 God is the same yesterday, today, and forever. His law of witnesses still stands, and is also applicable to scripture. We need additional scripture to add to the testimony of the Bible. And we believe that God continues to give scripture today.
I challenge all who read this to carefully study the Book of Mormon, and search to find if it is the word of God. In addition to careful study and pondering, I would implore you to ask God if these things are true. God is the ultimate source of truth, and can reveal these things to those who earnestly seek. We must have faith, and trust that God will lead us in to all truth. The Holy Ghost can confirm the truth of all things to us.