Is there any java library which can be used for converted Microsoft Word files (doc/docx) to Open Document Text format(.odt) formats. Free library would be preferable.
I don't know about any libraries that do it directly, but it should be relatively easy to exact the bits you're interested from a .docx using poi:
and then write them to an ODT format using ODFDOM:
http://incubator.apache.org/odftoolkit/odfdom/index.html
This should be relatively straightforward for simple documents, but if your use case calls for complex doucments containing pictures etc, this might become a LOT harder.
Anyway, hope this helps at least some ;)