This is the 2406th most frequent Russian word.
официальным
The Russian word "официальным" means "official" in English.
The word "официальным" is used here as an adjective in the instrumental case, reflecting the official status of the document.
Этот документ является официальным подтверждением.
This document is an official confirmation.
Here, "официальное" is the nominative singular neuter form of the adjective, describing the status of position.
Он занимает официальное положение в компании.
He holds an official position in the company.
In this sentence, "официальным" is used as an instrumental case adjective describing the 'source.'