I could meet the phrase ものとする in some documents, agreements. I understand, the sentences with ものとする as a whole one, but I don't know anything about this very phrase. Which meaning does it exactly add to the sentence and in which situation I could use it?
...ものとする is a legal turn of phrase you frequently find in legal documents, business contracts and legal agreements in such a way:
ー This agreement shall be governed by, and construed and enforced in accordance with the law of Japan.
ー Notice of a change of address shall be effective only upon receipt of concerned parties.
ー The Purchaser and the Seller will respectively pay all fees and expenses incurred by them in connection with the transaction contemplated hereunder.
ー Both Company and Distributor shall periodically furnish information and market report each other to promote the sale of product.
"ものとする" can be interpreted as "It is agreed upon" or "It is stipulated," but there's no problem if you dispense with it in a clause, and as you see, it will not make any difference on the purport of text.
Personally I don't like this redundant expression, which is simply an antiquated and superficial legal cliche, but lamentably it's still being used ubiquitously in legal documents.This is nothing more than a tool for lawyers to charge their clients an extra and exorbitant fee for cosmeticizing their clumsy legal documents with patina.
A reminder: There are other usages resembling "ものとする." That is ものに(or と)する, which is irrelevant to legal statements, and used to mean:
(1) to make sth one's own possession, e.g.
彼は社長の地位を物（もの）にした - meaning "He won the position of president."
(2) to take a good command of sth, e.g.
彼は英語を物（もの）にした - meaning "He mastered English language."