V4 works in P5. Not all material options are supported in P5, however. 
When you try loading V4 into P5, you'll get a message that it was meant for a newer version of Poser. P5 will try to load it anyway, and it will succeed. 
Same goes for P4: V4 will still work in P4, but many material options are lost. 

By the way, the P4 woman is usually called Posette.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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