Does the Book of Mormon replace the Bible? Doesn’t the Bible contain all of God’s word?
The Book of Mormon does not replace the Bible in any way. As a believer and follower of Christ, I want to read as much scripture as I can. I want the assurance that both really are scripture, and the assurance of any further clarification on the word of God.
The Book of Mormon is a book of scripture, similar to the Bible. The Bible contains the writings of ancient prophets in the old world, roughly spanning from the creation to AD 100. The Book of Mormon contains the writings of ancient prophets on the American continent, roughly spanning 600 BC to AD 400.
We know God is God to all, and there is no way that this loving Heavenly Father would reveal his word to some children and not others. Both scriptures testify of Jesus Christ, and teach us both history and the word of God as given to man and lived by man throughout that history.
And so, we believe the Book of Mormon to be the word of God just as we believe the Bible to be the word of God (as far as it is translated correctly). Which is handy. The Book of Mormon proves that the Bible is the word of God. It completely supports and compliments it – as it should, if it really were the word of God. It also clarifies and further explains some parts of the Bible, and vice versa.
But behold, there shall be many… of the Gentiles shall say: A Bible! A Bible! We have got a Bible, and there cannot be any more Bible.
But thus saith the Lord God: O fools … Know ye not that there are more nations than one? Know ye not that I, the Lord your God, have created all men, and that I remember those who are upon the isles of the sea; and that I rule in the heavens above and in the earth beneath; and I bring forth my word unto the children of men, yea, even upon all the nations of the earth?
… Know ye not that the testimony of two nations is a witness unto you that I am God, that I remember one nation like unto another? Wherefore, I speak the same words unto one nation like unto another. And when the two enations shall run together the testimony of the two nations shall run together also.
And I do this that I may prove unto many that I am the same yesterday, today, and forever; and that I speak forth my words according to mine own pleasure. And because that I have spoken one word ye need not suppose that I cannot speak another; for my work is not yet finished; neither shall it be until the end of man, neither from that time henceforth and forever.
Wherefore, because that ye have a Bible ye need not suppose that it contains all my words; neither need ye suppose that I have not caused more to be written.
For I command all men, both in the east and in the west, and in the north, and in the south, and in the islands of the sea, that they shall write the words which I speak unto them; for out of the books which shall be written I will judge the world, every man according to their works, according to that which is written.
(2 Nephi 29:1-11)
“But why is the Book of Mormon so essential if we already have the Bible to teach us about Jesus Christ? Have you ever wondered why there are so many Christian churches in the world today when they obtain their doctrines from essentially the same Bible? It is because they interpret the Bible differently. If they interpreted it the same, they would be the same church...” 
“The Bible is one witness of Jesus Christ; the Book of Mormon is another. Why is this second witness so crucial? The following illustration may help: How many straight lines can you draw through a single point on a piece of paper? The answer is infinite. For a moment, suppose that single point represents the Bible and that hundreds of those straight lines drawn through that point represent different interpretations of the Bible and that each of those interpretations represents a different church.
What happens, however, if on that piece of paper there is a second point representing the Book of Mormon? How many straight lines could you draw between these two reference points: the Bible and the Book of Mormon? Only one. Only one interpretation of Christ’s doctrines survives the testimony of these two witnesses.” 
That is the cool thing about this is: this book is a brilliant example of God’s “system of plural witnesses” . For every major event or anytime doctrine is being revealed to man, there has always been more than one witness to testify of it.
In the mouth of two or three witnesses shall every word be established.
(2 Corinthians 13:1)
There were both wise men and shepherds called to witness the birth of the Saviour.
When the Saviour was resurrected, He appeared to Mary, the two men on the road to Damascus, and the apostles – all to be witnesses and testify of His resurrection.
There are three members of the Godhead – God the Father, His Son Jesus Christ, and the Holy Ghost – and as separate beings, they witness and testify of each other all the time.
The Book of Mormon testifies of the Bible, and the Bible testifies of the Book of Mormon. Together, they are witnesses of Jesus Christ.
 and  Read this or watch the clip below.
 Jeffrey R. Holland, ‘”For a Wise Purpose”’, Ensign, Jan. 1996
How can I know if the Book of Mormon is true?
Simple. Put it to the test.
I’ll post more on this particular question later this month, but know this: you are entitled to know the truth of all things. Such knowledge is obtained through the Holy Ghost. Whether you consider yourself worthy or not, baptised or not, a Christian or not, you are a child of God and you are able to know the truth of these things.
Toward the end of the Book of Mormon, there is a scripture that explains:
And when ye shall receive these things … 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.
And by the power of the Holy Ghost ye may know the truth of all things.
It is simple. Put it to the test. Read the Book of Mormon for yourself, and ask God to know if it is true or if it is not.
I'm a Mormon, and I too have put the Book of Mormon to the test. We are all encouraged to do so. I have read the words on the pages, and felt so uplifted and happy. I don't always feel that way from reading the Bible, and sometimes my understanding of Jesus Christ and his teachings is greater when I read both scriptures side by side.
If you wish to order a free copy, let me know or click here.
Feel free to read or listen to it here.