1. "Mr X has joined our company as PM." The verb is active voice (no "been") because the subject, Mr. X, is the one doing the joining, presumably of his own volition.
2. "Mr. Y has been promoted to Manager in our company." The verb is passive voice (there's a "been"), which means that Mr. Y is not the one doing the promoting -- he can't promote himself. That action has been visited upo