PF to New Employee - what is the timeline for considering probation as per laws?

I want to know if a professional(lawyer, ca, architect etc.) while employing a person in his trade has to pay PF from appointment date or after confirmation period?what is the timeline for considering such probation as per laws? Is it necessary to pay PF at all? When one hired turns an employee for such purposes?

If Lawyer's firm is covered under PF Act then from first day employee has to be covered under PF.

Thanks Sir, but when a new hired is considered an employee?
Regards

And what makes a firm covered under PF act?