They are separate entities.
Deuteronomy 31
24When Moses had finished writing in a book the words of this law from beginning to end,
25he gave this command to the Levites who carried the ark of the covenant of the LORD:
26“
Take this Book of the Law and place it beside the ark of the covenant of the LORD your God, so that it may remain there as a witness against you.
The Book of the Law was a book written by Moses, and it was placed BESIDE the ark of the covenant. This Book of the Law was later seen throughout Israel's history.
2 Kings 22
8And Hilkiah the high priest said unto Shaphan the scribe,
I have found the book of the law in the house of the LORD. And Hilkiah gave the book to Shaphan, and he read it.
9And Shaphan the scribe came to the king, and brought the king word again, and said, Thy servants have gathered the money that was found in the house, and have delivered it into the hand of them that do the work, that have the oversight of the house of the LORD.
10And Shaphan the scribe shewed the king, saying, Hilkiah the priest hath delivered me
a book. And Shaphan read it before the king.
11And it came to pass, when the king had heard
the words of the book of the law, that he rent his clothes.
12And the king commanded Hilkiah the priest, and Ahikam the son of Shaphan, and Achbor the son of Michaiah, and Shaphan the scribe, and Asahiah a servant of the king's, saying,
13Go ye, inquire of the LORD for me, and for the people, and for all Judah, concerning
the words of this book that is found: for great
is the wrath of the LORD that is kindled against us, because our fathers have not hearkened unto
the words of this book, to do according unto all that which is written concerning us.
Again, here:
Nehemiah 8
1And all the people gathered themselves together as one man into the street that
was before the water gate; and they spake unto Ezra the scribe to bring
the book of the law of Moses, which the LORD had commanded to Israel.
2And Ezra the priest brought
the law before the congregation both of men and women, and all that could hear with understanding, upon the first day of the seventh month.
3And he read therein before the street that
was before the water gate from the morning until midday, before the men and the women, and those that could understand; and the ears of all the people
were attentive unto
the book of the law.
4And Ezra the scribe stood upon a pulpit of wood, which they had made for the purpose; and beside him stood Mattithiah, and Shema, and Anaiah, and Urijah, and Hilkiah, and Maaseiah, on his right hand; and on his left hand, Pedaiah, and Mishael, and Malchiah, and Hashum, and Hashbadana, Zechariah,
and Meshullam.
5And Ezra opened
the book in the sight of all the people; (for he was above all the people) and when he opened it, all the people stood up:
6And Ezra blessed the LORD, the great God. And all the people answered, Amen, Amen, with lifting up their hands: and they bowed their heads, and worshipped the LORD with
their faces to the ground.
7Also Jeshua, and Bani, and Sherebiah, Jamin, Akkub, Shabbethai, Hodijah, Maaseiah, Kelita, Azariah, Jozabad, Hanan, Pelaiah, and the Levites, caused the people to understand
the law: and the people
stood in their place.
8So they read in
the book in the law of God distinctly, and gave the sense, and caused
them to understand the reading.
Conversely, the 10 commandments were written with the finger of God upon two tables of stone, and they were placed INSIDE the ark of the covenant.
Exodus 31
18When the LORD had finished speaking with Moses on Mount Sinai, He gave him
the two tablets of the Testimony, tablets of stone inscribed by the finger of God.
The LORD instructed Moses to place " the Testimony" INSIDE of the ark of the covenant.
Exodus 25
16And
place inside the ark the Testimony, which I will give you.
Later on in Israel's history, when the ark of the covenant was brought to Solomon's temple, there was nothing found within it but the two tables of stone upon which were written the 10 commandments.
1 Kings 8
[
1] Then Solomon assembled the elders of Israel, and all the heads of the tribes, the chief of the fathers of the children of Israel, unto king Solomon in Jerusalem, that they might bring up the ark of the covenant of the LORD out of the city of David, which is Zion.
[
2] And all the men of Israel assembled themselves unto king Solomon at the feast in the month Ethanim, which is the seventh month.
[
3] And all the elders of Israel came, and the priests took up the ark.
[
4] And they brought up the ark of the LORD, and the tabernacle of the congregation, and all the holy vessels that were in the tabernacle, even those did the priests and the Levites bring up.
[
5] And king Solomon, and all the congregation of Israel, that were assembled unto him, were with him before the ark, sacrificing sheep and oxen, that could not be told nor numbered for multitude.
[
6] And the priests brought in the ark of the covenant of the LORD unto his place, into the oracle of the house, to the most holy place, even under the wings of the cherubims.
[
7] For the cherubims spread forth their two wings over the place of the ark, and the cherubims covered the ark and the staves thereof above.
[
8] And they drew out the staves, that the ends of the staves were seen out in the holy place before the oracle, and they were not seen without: and there they are unto this day.
[
9]
There was nothing in the ark save the two tables of stone, which Moses put there at Horeb, when the LORD made a covenant with the children of Israel, when they came out of the land of Egypt.
So, again, the Book of the Law was a book written by Moses, which was placed BESIDE the ark of the covenant whereas the 10 commandments were written with the finger of God upon two tables of stone, which were placed INSIDE the ark of the covenant.