Can a debt collector file and execute a lawsuit without your knowledge?

You have to be served with the summons and complaint (the complaint is the lawsuit attached to the summons) after the lawsuit has been filed with the court.  Until you are served with the summons and complaint, you have not been notified of the lawsuit.  After you are served with the summons and complaint, you will need to file with the court an answer to the complaint within the time set forth in the summons and serve by mail a copy of your answer to the complaint on the opposing party or the opposing party's attorney.  If you don't timely file your answer to the complaint with the court and serve it by mail on the opposing party within the time set forth in the summons, the opposing party can get a default judgment entered against you.  A default judgment means you have lost.  If that occurs, you will need to file a motion to set aside the default.  If the court grants your motion to set aside the default, the case is then back on track and litigation will continue.

If the opposing party claims you were served with the summons and complaint when in fact you were never served, you would have a strong argument to support your motion to set aside the default.