A lot of word-processing software support both the DOCX format from MS Word as well as the OTT format from OpenOffice.org and as such, it should be easy enough to convert DOCX to OTT.
Convert Microsoft Word Open XML document to OpenOffice.org text document template.
We have found 5 software records in our database eligible for .docx to .ott file format conversion.
Microsoft Windows software - convert docx to ott on Windows
A free word processing program, part of GNOME office productivity bundle
Convert from docx file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned docx to ott. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A reliable word processor from SoftMaker Office suite
Linux/Unix software - convert docx to ott on Linux
An open source word processor for Linux
Multiplatform software - convert docx to ott on any platform
Word processor and text editor from OpenOffice.org suite
Full-featured word processing and desktop publishing tool from LibreOffice suite