Annual Tax Return

A neighbour has asked me to help with their annual tax return for their condo owned in a company name. All seems pretty straight forward, the only thing I'm not clear about is if he can sign it himself under "Juramento del Declarante" or if it is necessary to have it completed and/or approved by a bookkeeper/accountant etc and signed under "Autorizacion de Representacion" Tried searching here and website but no joy.

Thanks,
Linda.