For the purpose of treating Employer's contribution towards provident fund as deducitble expense, while determining total income of the employer,it is necessary that the provident fund should must be registered.
The registration procedure of P.F is provided in the taw law see schedule 6 of Income Tax Ordinance,2001.
But you should keep it in mind that a trust deed is essential document for P.F. The detailed procedure of registration and recognition of P.F is available in almost all books on taxation.