What was the reasons for documentary hypothesis? Documentary Hypothesis assumes that the text of the Torah as
  preserved can be divided into identifiable sources that predate its
  compilations by centuries, the Jahwist (J) source being the oldest,
  dating to as early as the 10th century BCE, along with the Elohist
  (E), the Deuteronomist (D), and the Priestly source (P), dating to the
  8th to 6th centuries. The final compilation of the extant text is
  dated to either the 6th or 5th century BCE.


What specific verses or parts of Pentateuch drive to the above hypothesis?
The hypothesis was formed from several lines of evidence suggesting that more than one author had a hand in writing the Torah.

Stage 1

The first stage was the recognition of certain passages that looked like additions from a later copyist:


Deuteronomy 34, the account of Moses' death, including the phrase in verse 6, "no one knows his burial place to this day."
Genesis 12:6, "At that time the Canaanites were in the land." And they still were when Moses died.
Numbers 21:14, referring to "the Book of the Wars of the Lord", which would have been written after the Torah
Numbers 12:3, stating, "Moses was very humble, more so than anyone else on the face of the earth," which would not have been true if he had written it himself.


Stage 2

The second stage was the discovery of "doublets", stories that appeared in two forms, with differing details that included one version using Elohim to refer to God, and the other version using YHWH. Examples include:


Creation: Genesis 1:1 - 2:3 ("six days", Elohim); Genesis 2:4-25 ("Garden of Eden", YHWH)
God's covenant with Abraham: Genesis 15:1-21 (YWHW); Genesis 17:1-27 (Elohim, though it refers to YWHW in verse 1)
Abraham calls his wife his sister: Genesis 12:10-20 (YHWH); Genesis 20:1-18 (Elohim, though it uses YHWH in verse 18)


And then there are doublets that don't fit the YWHW/Elohim pattern, but appear reflect two distinct traditions:


God renames Jacob to Israel: Genesis 32:22-32 (after wrestling God at Peniel); Genesis 35:9-15 (at Bethel)
Moses' father in law: Exodus 2:17-22 (Zipporah's father is Reuel); Exodus 18:1-6 (Zipporah's father is Jethro)
Covenant of the Ten Commandments: Exodus 34 (on Mount Sinai); Deuteronomy 5 (on Mount Horeb) &mdash; Deuteronomy 5 is written as a reminder of the covenant from Exodus 34


Stage 3

The third stage was the development of the documentary hypothesis itself. Scholars identified what they believed to be four sources, which they labeled J, E, P, and D.


J: these always used YHWH to refer to God (most of the scholars were German, and German J = English Y)
E: these almost always used Elohim (or a related form, e.g. El Shaddai or El Elyon) to refer to God
P: these passages referred to matters relating to Priests
D: the book of Deuteronomy was considered to have its own distinct source