There are different types of files for poser content.

cr2 is for figures and conforming clothing

pz2 is for Poses and character morphs (parameters that will change the shape of your figurer.)

fc2 is for expressions and faces

hr2 is for hair

hd2 is for hand poses

pp2 is for props and dynamic clothing

lt2 is for lights

Cm2 is for camera angles

Mt5 and Mc6 are for materials. Mt5 is for a single material usually able to be applied to anything. Mc6 is for adding several materials and is specific to a certain figure or prop.

and Pz3 is for scene files.

As Ohki said, they are all loaded from the poser library rather than outside of Poser

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