Document.XMLSaveThroughXSLT (Word)

Sets or returns a String that specifies the path and file name for the Extensible Stylesheet Language Transformation (XSLT) to apply when a user saves a document.

The XMLSaveThroughXSLT property is only applicable when the XMLUseXSLTWhenSaving property is set to True. If the XMLUseXSLTWhenSaving property is set to False, Microsoft Word will ignore the XMLSaveThroughXSLT property.

ActiveDocument.XMLUseXSLTWhenSaving = True 
ActiveDocument.XMLSaveThroughXSLT = "c:\schemas\book.xsl"