For an employee Form-16 is a important document containing the details of salary ,deductions considered by employer, TDS already deducted etc. Form 16 is helpful, but it is not required in order to file an ITR.
If it isn't there, you can still file your ITR by gathering substitute paperwork and relevant information about your income and taxes. Compiling payslips, bank statements, and other relevant financial documents facilitates income and tax computation.