Please read Where can I find itext.dtd?
I'm the original developer of iText and I'm also the one who once upon a time, long ago, wrote the DTD for the iText XML files. That was even before XSD existed, so it's a really long time ago!
Support for this DTD has been removed from iText (I believe that was about when my first book was released in 2006) in favor of other ways to convert XML to PDF. It's very surprising to see that obsolete XML appear in something called RazorPDF.
In any case: I'm the CEO of the iText group, responsible for iText and iTextSharp, and I don't know anything about RazorPDF. I'm pretty sure RazorPDF uses a mighty old version of iText and my answer to this question explains why it shouldn't: https://stackoverflow.com/questions/25696851/can-itext-2-1-7-or-earlier-can-be-used-commercially