Generating such documents is very simple with RPE: specify the output document’s extension to be either .docx (Word Document in Open Office XML format ) or .docm (Word Macro-Enabled Document). Use .docm if you need to run macros.
See this for a list of Microsoft Office 2007 filename extensions
NOTE: RPE does not support Office 2007 files as stylesheets. This includes .dotx, .dotm and .docx.