Stefan suggested I post this question here:
Does anyone know of an easy to use way to convert from .doc to .docx on the linux commandline? I want something scriptable and easy to use.
abiword --to=docx foo.doc
should work, but produces an empty docx file.
There are some utilities out there using openoffice such as http://www.oooninja.com/2008/02/batch-command-line-file-conversion-with.html but this seems to have a problem with docx.
(For the record loading it up in openoffice and saving it as docx works but isn't viable for scripting.)
Any suggestions appreciated.