I'm pleased to announce that (clause)

This is a very formal phrase that you use when making announcements to large groups. You can use this in writing, or when speaking on stage in front of an audience. You can imagine the president of a country using this phrase when giving a speech: My fellow Americans, I'm pleased to announce that today, due to our efforts, a nuclear showdown has been averted with North Korea. This phrase is used in business settings for formal announcements that are sent out to the company about new employees, promotions, good quarterly results, awards, and so on.

(someone) has been promoted to (job title)

When you give someone a promotion (which is a job with a higher title or pay), you shouldn't say "I promoted Carlos..." That sounds too self-centered, like you're trying to take the spotlight away from this person.

It's better to say "Carlos has been promoted..." In this way, you can describe a person's promotion without saying who did it. In general, when you don't want to say who did an action, you say "___ was ___ed".

regional manager

A "region" is a certain area of a country, continent, or of the world. The "regional manager" is someone in a company who's in charge of a region:

I'm the regional sales manager for our Asian offices.