A Muslim will always discount the Bible saying it has been changed and corrupted from the time Allah gave it to his prophets. They first need to understand that we use different English translations from the original Hebrew and Greek. Muslims often compare different translations of the Bible or point out the varying texts in the New Testament and Apocrypha. There are also different "versions" of the Quran, but these are not like the Bible's different versions.
There are 7 variants (or forms) of the Quran, but these variants are in the way you recite the Quran. Essentially the 7 forms of recitation come from different vowel pointings in later manuscripts. The original written Arabic did not have vowels. A Muslim will say that there is no difference in these recitations and that the Quran has been preserved, even though a word can change with different vowel pointings.
In order to avoid long debates about textual criticism of the Bible versus the Quran, it is best to compare the "7 forms of recitation" of the Quran with the textual variants in the Bible. We can say that there have been no doctrinal differences because of these variants in the Bible and Quran, and today they are both in their original form. Ultimately though, textual and historical evidence finds the NT exceptionally reliable. Refer to any Christian apologetic materials on textual criticism. If a Muslim still persists on the corruption of the Bible, a harsh response is to bring up the differences between Shi'a and Sunni texts in the Quran.
Logically, if the Bible was ever God's Word, then God would not have allowed it to have changed. The Quran clearly states that the Bible is clearly God's Word. Ask your Muslim friend to answer the following questions. (1) How can the Quran confirm a Book that has been changed? (2) How can the Bible be used as a proof text and foundation for the Quran when the Bible has been altered? (3) If the Bible is God's word, how is it possible for man to change His eternal and unchangeable Word? (4) Why does the Quran mention the Bible (OT, NT, prophets) when the Bible does not explicitly reference Muhammad or the Quran? (5) Jesus himself said His Words would never be changed (Matthew 24:35). Both Isaiah the prophet and 1 Peter declare "the word of the Lord stands forever." (1 Peter 1:23-25 and Isaiah 40:8)
Quran 3:3-4: It is He Who sent down to thee (step by step), in truth, the Book, confirming what went before it; and He sent down the Law (of Moses) and the Gospel (of Jesus) before this, as a guide to mankind, and He sent down the criterion (of judgment between right and wrong). Then those who reject Faith in the Signs of Allah will suffer the severest penalty, and Allah is Exalted in Might, Lord of Retribution.
Quran 3:78: Among them are those who twist their tongues to imitate the scripture, that you may think it is from the scripture, when it is not from the scripture, and they claim that it is from Allah, when it is not from Allah. Thus, they utter lies and attribute them to Allah, knowingly.
Quran 4:163: We have sent thee inspiration, as We sent it to Noah and the Messengers after him: we sent inspiration to Abraham, Ishmael, Isaac, Jacob and the Tribes, to Jesus, Job, Jonah, Aaron, and Solomon, and to David We gave the Psalms.
Quran 5:15: O people of the Book! There hath come to you our Messenger, revealing to you much that ye used to hide in the Book, and passing over much (that is now unnecessary). There hath come to you from Allah a (new) light and a perspicuous Book,
Quran 10:64: For them are glad tidings, in the life of the present and in the Hereafter; no change can there be in the words of Allah. This is indeed the supreme felicity.
Muslims believe that the preachings of Moses (referred to in the Quran) were the revelation of God, but that the Torah in our Bible is not that revelation. They believe that the Biblical Torah has another author. In the same way, the Psalms of the prophet David (referred to in the Quran) have been corrupted by Christian scholars. Likewise the Gospel that Jesus the prophet preached (also in the Quran) is not in our Christian NT. They point out the fact that of the 27 books of the NT, only a handful are the words of Jesus. Those books containing the words of Christ are entitled the Gospels of Mathew Mark, and Luke, but there is no Gospel of Jesus in the NT. A Muslims understanding of God's Word is that it will always come through a prophet in book form. Therefore they will typically ask if Jesus carried His gospel around with him when he preached. Muslims have misunderstood the whole canon process, and they assume that the Gospel at the time of Jesus was the book he carried with him, and not the epistles of the NT.
Quran 4:125: "Whose religion is better than one who SUBMITS himself to God, works righteousness and follows the faith Of Abraham the monotheist? God has chosen Abraham as a beloved friend".
On another note, SOME WIll try to change our behaviours at work etc... I know someone that had one approach him at work and tell him to put tape or something on a calendar girl. as it bothered him to see naked skin everyday when he has to pass his desk. Which that ended up with him lecturing him about islam and how it is so bad and wrong to view female flesh/skin. I do wonder why some of them can be so sexist and think that women do not view mens flesh and they do not have to cover themselves up head to toe also. I bet a male on a calendar in only a pair of ripped jeans would not be so bothersome.