1) e-Returns of all corporate assessee's has to be signed using digital signature.This has been made mandatory w.e.f 9/7/2010 vide CBDT notification 49/2010.
18 July 2010
as per notification no. 49, efiling with or without digital signature is mandatory for partnership firm or prop/individual whose accounts are liable to be audited under section 44AB. Thus partnership firm if section 44AB is not applicable may file its return in paper form. for corporate Digital signatures are mandatory as replied above.