I can't think of a clearer way to put it than this. Basically it's an official notification with several named recipients, and, since it comes from within a very bureaucratic-oriented company, they give it a special name (I can only assume this has some arcane purpose outsiders are unconcerned with). Personally, I wouldn't worry too much stylisically about the administratve nomenclature you use beyond questions of accuracy and consistency within or between the documents you are translating (assuming they are Pemex documents, there is no "right" way to translate them), and just focus on getting the legal and technical terminology correct.