All Poser 4, 5 and 6 content works in Poser 7. 
All scenes created in Poser 4,5 and 6 work in Poser 7.

Some gotchas:

• the scenes reference figures, props, textures and geometries. Those must be present in one of the (external) runtimes that Poser 7 knows about. 
• some Poser 5 material nodes have a different implementation in Poser 6 and 7. For example, the Cell node has a Scale parameter in Poser 5, while it has separate xScale, yScale and zScale parameters in Poser 6 and 7. 
• some of the very old Poser 4 (not ProPack) scenes refer to .BUM files for bump maps (actually, they're normal maps). I'm not sure whether Poser 7 handles .BUM files correctly.

There's a lot that's not perfect in Poser. But they got their backwards compatibility right. It just plain works.

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