Paul’s use of the Old Testament is very evident in the book of Romans. There are 50 references to Old Testament Scriptures from thirteen different books. Paul does not seem to quote Scripture verbatim every time he refers to it. Paul paraphrases and contextualizes the Scriptures. One example of this is in 2:24:

For, “THE NAME OF GOD IS BLASPHEMED AMONG THE GENTILES BECAUSE OF YOU,” just as it is written. (NASB)

The Old Testament reference is Isaiah 53:5 which states:

Now therefore, what do I have here,” declares the LORD, “seeing that My people have been taken away without cause?” Again the LORD declares, “Those who rule over them bowl, and My name is continually blasphemed all day long. (NASB)

There are other times where he does give verbatim when he refers to the Ten Commandments and Exodus and Deuteronomy when to not covet, etc. (i.e. Rom 7:7). Paul will refer to certain personalities and books depending on what he is addressing, when he addresses Israel in chapter 9, it is mainly the prophetic books. When dealing with the word of faith and salvation in chapter 10, Paul usually sticks to the historical books. If Paul referred to any one personality the most, it would be Abraham when he is justified in his faith and to the prophet Isaiah as he refers to him thirteen times (tied with the most references with The Psalms).