Effects of molecular weight (L-c) and field strength (E) on conformation of polymer chains and their density are investigated at the surface and bulk of a driven chain system in three dimensions with a Monte Carlo simulation. As the polymer chains deposit on the surface, a linear density gradient develops in low field. While the gradient becomes steeper on increasing the field in low L-c, onset of oscillation in the polymer density profile appears with higher L-c, above a characteristic value of field (E-c) which decreases with increasing molecular weight. The substrate coverage (theta (j)) exhibits a rapid increase on increasing the Field and tends to decline at high fields. In the bulk, the polymer density decreases rapidly with the molecular weight while the substrate coverage (theta (j)) decays exponentially, theta (j) similar to e(-beta Lc). The radius of gyration (R-g) of chains undergoes a crossover from SAW to rodlike conformation in the bulk on increasing the field. On the surface, chains are longitudinally compressed with a sub-SAW conformation, i.e., the scaling exponent v similar to 0.50 - 0.55(R-g similar to L-c(-v)). Nonmonotonic response with opposite trend is observed in the variation of the longitudinal (minimum) and transverse (maximum) components of the radius of gyration with the field.