This work generalizes Li-Kardar functional integral approach to a smectic film, wetting the boundary of the isotropic liquid phase. Isotropic-smectic A (IA) interface is considered as an ointernalo (bulk) boundary of the film. Previously we generalized this approach to the wetting smectic film with so called Neumann boundary condition, where normal gradients of the smectic layers' displacements at distorted IA-interface were suppressed. In the present paper a nontrivial boundary condition of the vanishing normal forces at the fluctuating IA-interface is considered. Elastic, fluctuation-induced effects for the wetting smectic film with this boundary condition are found.