1 .  Paul had a very high view of the inspiration of the Old Testament:

           All scripture is inspired by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work (2 Tim 3:16-17).

This reverence for the Jewish Scriptures (Tanakh) is reflected in his frequent citations of Bible verses in many of his letters.  Romans and Corinthians, especially, are chock full of Scripture references from many books, including the Pentateuch, Psalms and several prophets.  This is all the more notable since these letters were written to congregations with a large Gentile constituency.  He assumed in his readers a familiarity with Bible history, theology, and religious leaders. 

           

Specifically, in Romans he writes extensively about sin, the Law, circumcision, Moses, and Israel, quoting from Genesis, Exodus, Deuteronomy, Isaiah and other prophetic books, and Psalms.  In the Corinthian books, he refers to the Exodus, Israel's rebellion in the wilderness (1 Cor 10), Moses and the veil over his face, and the Old Covenant.  He quotes from a wide range of Scriptures, scattering verses to illustrate his points -- the Pentateuch, Isaiah, Psalms, even Jeremiah, Ezekiel and Job.  In Galatians, he has a long discussion on the true sons of Abraham, and contrasts the "mothers" of the two covenants -- Sarah and Hagar.  These letters assume detailed knowledge of Jewish origins in his readers.

Some smaller epistles have very few or no Old Testament references -- Philippians, Colossians, Thessalonians, Titus.  The letters to Timothy perhaps give us the best summary of Paul's esteem for the Bible.  In addition to the passage quoted above, he says,

          Till I come, attend to the public reading of scripture, to preaching, to teaching (1 Tim 4:13).
    
           From childhood you have been acquainted with the sacred writings which are able to instruct you for salvation through faith in Christ Jesus (2 Tim 3:15).

Paul's attitude toward the Bible is similar to that of a contemporary evangelical Protestant...or a first century orthodox rabbi.  The written revelation is the foundation of belief.   Thus we must infer that much of his preaching to the Gentiles involved giving them a background in the Old Testament, as preparation for understanding the word and work of Jesus.