Form 26c

I think that is the return filing form for tds deducted on payments made to contractors and subcontractrs

Annual return of deduction of tax from payments made to contractors
or sub-contractors under section 206 of the Income-tax Act, 1961

Is it compulsory to file this return, if we have filed 26Q of all 4 quarter?

not necessary if u have filed 26Q, further you have to use this form