PDFsharp & MigraDoc Foundation

Migradoc handles merged PDF files excellent. However, there does not seem to be a provision to merge RTF files?

Here is a basic example of my system:
Users first can choose either PDF or RTF.
I make extensive use of styles, tables, and headings.
They pick a number of documents to print for a customer (typically invoices and remittance advice, etc).
After they have chose what they want, the system will then merge them into a single document.

For PDF, Migradoc handles this, but for RTF, I'm kind of at a loss. I've tried a few things such as the RichTextFormat box, and a few other tricks, but they all seem to lose headings, tables or formatting.

So far, I haven't found a good way to merge the RTF.