When I use an xsl-fo file produce with WordToFoConverter. 
There is an exception in Apache FOP because the xmlns of the xmpmeta element is not correct. 
hwpf generate :

<x:xmpmeta xmlns:x="adobe:ns:meta">
[...]
</x:xmpmeta>  

but apache FOP expect a slash ("/") at the end:

<x:xmpmeta xmlns:x="adobe:ns:meta/">
[...]
</x:xmpmeta>  

I have checked the specification (see http://partners.adobe.com/public/developer/en/xmp/sdk/XMPspecification.pdf, page 22)

I have modified FoDocumentFacade at line 245 like this :

 Element xmpmeta = document.createElementNS( "adobe:ns:meta/",
                "x:xmpmeta" );

And it works fine now.