What is the ruling on a man marrying a widow secretly, relying on an 'urfi contract signed by two witnesses, because she fears for her children's pensions?

Marriage is not Islamically valid except with conditions and pillars, including: the guardian (wali), witnesses, offer (ijab), and acceptance (qabul). Therefore, a marriage contract without the presence of the contract witnesses or the guardian is void, and you must separate from her. If you wish to marry her, you must enter into a valid contract with her guardian or his representative. Furthermore, documenting and registering the marriage contract with official authorities has become an urgent necessity in this era. It is not permissible to conceal a marriage as a ploy to obtain a salary that the married woman is not entitled to.