I have a question. Is it possible to file the paperwork for state primaries without officially announcing?
Not really. As far as I know, any candidate paperwork filed is public record, and here in Illinois it will be on the state board of elections website more or less immediately. This is so objectors can jump right in and try to knock people off the ballot, and I actually know of one objector here who will complain about candidate birth certificates.
So no, trying to file without announcing would really just be turning the announcement over to a hostile press, and there's no upside to that.
No.