Roman Catholics use it constantly on this Forum as "authoritative." In fact that's how i learned about it!
If it is not what the Roman Catholic Church approves of, please show it to us, but first of all to your fellow Roman Catholics.
It's an encyclopedia, i.e. a third level source. By third level, I mean two levels away from an original source on just about every subject that it covers. As third level sources go, I find it a very good one, in its own way on a par with Brittanica as opposed to World Book or Compton's. It is superior, I believe, to the New Catholic Encyclopedia as it tends to be more conservative and less "liberal" than the NCE. And it's a handy reference, being that it is online. But when all is said and done, it is ONLY a third level source. Some on this forum have used it as if it were more authoritative than that.
But it isn't a primary source and contains some errors that are forgiveable given its era.
It also contains some biases and interpretations of its editors that do not hold up to current scholarship of any stripe.
Encyclopedias that are not regularly updated eventually become useless. The Britannica for example is regularly updated and extraordinary in its scope and depth. This old Catholic Encyclopedia has no like method of updating, reevaluation, and addition.
The official teachings of the Catholic Church can be found in places you well know such as the Catechism and the two new Compendia. The Holy See has not authorised an Encylopedia though it would be a most worthy project.