Most Christian religions believe that there is no scripture outside of the Bible. However, most religious scholars will agree that many books of scripture were lost during the compilation of the Bible. In our religion, we believe that the Bible is the word of God as far as it is translated correctly. But we also believe that additional scripture could be found. We also believe that further revelation may come, and it should be included in modern day scripture.
Let's imagine that diggers at an archaeological site found additional writings of Paul. Would we immediately discount them simply because they weren't originally included in the compilation of the Bible? Why should we be afraid of truth? If it is scripture, then let it be. If it isn't, then we can discount it. But simply closing our eyes and refusing to read it, simply because it wasn't included in the original Bible, does not help us to be seekers of truth. Now let's imagine that we can't verify that Paul was indeed the writer. Do we wholely reject the writings? Or can we study them with the intent to see if there could be truth in them? We should never be afraid of truth, but should press forward relying upon the guidance of the Holy Ghost to help us to discern truth from error. A scripture in the Book of Mormon teaches more about this idea:
"6 And whatsoever thing is good is just and true; wherefore, nothing that is good denieth the Christ, but acknowledgeth that he is.
7 And ye may know that he is, by the power of the Holy Ghost; wherefore I would exhort you that ye deny not the power of God; for he worketh by power, according to the faith of the children of men, the same today and tomorrow, and forever.
8 And again, I exhort you, my brethren, that ye deny not the gifts of God, for they are many; and they come from the same God. And there are different ways that these gifts are administered; but it is the same God who worketh all in all; and they are given by the manifestations of the Spirit of God unto men, to profit them." Moroni 10:6-8
In our religion we have additional scripture. We embrace the Bible as the word of God. We study it, we love it, we revere it. But we do not believe that God has closed His mouth. We have the Book of Mormon which we believe is scripture that came from those who lived in the ancient Americas. We believe that after Christ arose from the dead, that He visited these people in the Americas, and gave them His Gospel. The Book of Mormon contains a very important promise. It says,
"3 Behold, I would exhort you that when ye shall read these things, if it be wisdom in God that ye should read them, that ye would remember how merciful the Lord hath been unto the children of men, from the creation of Adam even down until the time that ye shall receive these things, and ponder it in your hearts.
4 And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost.
5 And by the power of the Holy Ghost ye may know the truth of all things." Moroni 10:3-5
I would encourage you to follow this promise. Do not discount the Book of Mormon simply because it wasn't included in the Bible. Do as it's writers ask and read it with pure intent, having faith in Christ that He will guide you to know if it is true. You can read it online by clicking here or you can click here to find information about how you can get a free copy.
I hope that you will study it with the intent to know if it is true. Those who read it with the intent to "prove it wrong" are not those who are honest seekers of truth. The Holy Ghost will help those who are humble, and who ask God for help in discerning.