The MSDN forums are for programming questions. You should ask this in the end-user forums, where you're more likely to find people who work with RTF:
http://answers.microsoft.com/en-us/office/forum/word
When you ask you MUST specify the version of Word you're using.
FWIW, however, Microsoft has discontinued the RTF file format; it's been superceded by the new Office Open XML file formats. This means that, if things change in newer versions of Word, they probably won't be supported in RTF, which could lead to problems.
Cindy Meister, VSTO/Word MVP,
my blog