Who is required to file an Annual Return? In what format such return should be furnished? What is the due date for furnishing such return

All registered taxable persons are required to furnish an Annual Return for every financial year, electronically, in FORM GSTR-9. A registered taxable person paying opting to pay tax under the composition scheme is required to file the annual return in FORM GSTR-9A. However, the below mentioned registered taxable persons are not required to file an Annual Return:-
(a) Input Service Distributor
(b) Person liable to deduct tax at source as per Section 51 (for the purpose of TDS)
(c) Person liable to collect tax at source as per Section 52 (for the purpose of TCS)
(d) Casual taxable person
(e) Non-resident taxable person .Such returns should be furnished on or before 31st December of the following the end of financial year.

(ICAI FAQ PUBLICATIONS 06-09-2017 RETURNS : FAQ NO. 50)