Hello,
As you're using Debian x86_64 and the included version of OpenOffice is for 32 bits, you can use this version installing ia32-libs and uno-libs3 packages or install your own version of OpenOffice. Please note that if you're missing of a shared library you can find in which package is included on this page: http://packages.debian.org
This info is the same you can find on page http://www.phpdocx.com/help/conversion-plugin-docx-to-pdf
Regards.