Hi Tim,
Thank you for your update.
Sorry for the long delay in responding.Currently DocIO do not have support for programatically adding the mergeformat in the document. It can only preserve the mergeformats in the document.We have created the sample for your understanding.Could you please find the sample from the below link.Try running the sample and let us know if this helps.
Sample link:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=F94199-495929788.zipPlease let us know if this helps.
Regards,
Poornima