Hi An,
XLIFF is just a format to represent the original document split in translation units.
You can go to and from the original format in different ways: going XML -> XLIFF -> XML, is easier because XSLT can be used; for other formats you have to find ad-hoc solutions.
Look explicitly for a Word to XLIFF converter, or maybe use the Open Document Format (e.g. ODT) in Libreoffice and rely on odf2xliff:http://translate-toolkit.readthedocs.org/en/latest/commands/odf2xliff.html
Ciao, Antonio