Hi there, while working with VcgLib i figured out normal maps arent supported for the OBJ import/export
the "norm" attribute isnt featured in the official OBJ format specs, but has been extended for physically-based rendering in various softwares
read more here from @bhouston

Pr/map_Pr     # roughness
Pm/map_Pm     # metallic
Ps/map_Ps     # sheen
Pc            # clearcoat thickness
Pcr           # clearcoat roughness
Ke/map_Ke     # emissive
aniso         # anisotropy
anisor        # anisotropy rotation
norm          # normal map (RGB components represent XYZ components of the surface normal)

is that an extension that VcgLib authors would consider ? having normal map read / write feature would be usefull,
thx