Folks, ISO/IEC 29500-1:2006 (OOXML) uses application/x-font-ttf for opentype, and we have decided not to change it. But I learned that some documents from Microsoft use application/vnd.ms-opentype as media types for opentype fonts. http://msdn.microsoft.com/en-us/library/system.io.packaging.packagepart.contenttype.aspx Cheers, Makoto