Ex Employer sent a "legal notice" on email

Hello all, I need help to understand whether a notice sent on an email by the HR of an employer on a word document which is not having a digital signature also, can this document be considered as a legal notice and whether it warrants any action? If yes what should we do? just a heads up here it is a legal notice by an employer to an ex-employee after 4 months of leaving the company and giving due notice period. Now the employee has sent an emailed a notice document through an HR as a PDF so should this be counted as a legal notice and reverted legal or no action is required,?