Microsoft Word stores questions in a format called Office Math Markup Language (OMML). On import to Moodle using the WordTable plugin, the questions are converted into MathML. The conversion is very good, but not perfect. To display MathML correctly inside Moodle, you must use the MathJax filter (Site administration > Plugins > Filters > MathJax), and insert "<math" into the Additional equation delimiters field.
To edit MathML inside Moodle, the default Equation Editor built in to the Atto text editor is not enough, I think. You probably need to install a 3rd-party equation editor like WIRIS.