The physical properties of a polycarbonate (PC) glass formed under high pressure are evaluated experimentally and compared to molecular dynamics simulations of a simple model polymer capable of pressure densification. Pressure densified glass (PDG) exhibits higher enthalpy and is as much as 4% denser than the corresponding glass formed at ambient pressure. Measurements of the first sharp diffraction peak reveal that local density fluctuations are suppressed in PDG, as corroborated by elastic incoherent neutron scattering measurements. Both the experimental and simulation results indicate that the reduced stability of PDG limits the pressures for which pressure densification is effective; at too high a pressure the glass transition temperature falls below ambient.