My guess is PRESS-RELEASES: These are official statements sent by organisations to inform the public and media about something noteworthy or that they want people to know about.

• It is a 13- letter word
• It is public and official: it is an office statement sent the public(media)
• It is informative: In the sense that it makes the people to be in the know about what is about to happen either in a country, state,or or an organization.
• It can be seen and can be heard: it can be seen when writing it on a paper,or broadcasting on the television, then it can be heard when announcing on the radio or through dialoguing.