Summary: At present, EMF files are best converted to SVG using OpenOffice.
Note regarding options for converting EMF files to SVG and/or PNG
(as at Feb 2010):
(Could mono's libgdiplus help? Search for 'mono metafile')
wmf2tosvg is a good solution for WMF, but it has no EMF support.
FreeHEP has EMF2SVG, but the output wasn't much good (perhaps
because office drawings aren't its primary focus). It would
also be a very complex dependency.
Batik has WMFTranscoder, but not EMFTranscoder! It looks like
one could be added from package
with a bit of work, but still, batik is no good on appengine since
it uses awt, and spawns threads. So avoid it..
imagemagick has no support for EMF at all (other than on Windows).
openoffice can be used to convert EMF; I found it worked well.
Until the EMFParser in com.adobe.dp.office is fixed, this may be
a good option (depending on your environment).
Maybe the code to use openoffice for EMF conversions could go in
src/docx4j-extras, so only those who wanted to use it would need
to worry about the dependencies.
TODO: Have a look at cairo, which has java bindings. Can it be used
to read EMF? See also pymfvu - UniCovertor will ultimately be able
to import EMF