When you save a file as a PDF file or as a XPS file in Microsoft PowerPoint 2010, in Microsoft Word 2010, or in Microsoft Office Word 2007 on a Windows XP-based computer, the equations are not saved.
To work around this issue, follow these steps:
Click Start, and then click Run.
Type intl.cpl in the Open box, and then click OK.
In the Regional and Language Options dialog box, click the Languages tab.
In the Supplemental language support section, click to select the Install files for complex script and right-to-left languages (including Thai) or Install files for East Asian languages check box.