Q: Can jPDFWriter be used to print RTF documents to PDF?
A: Yes, you can use jPDFWriter to do this. Take a look at the loadRTF document method in the PDFDocument class.
jPDFWriter does not do the actual rendering of the RTF files. The library uses standard Java classes to load and render rtf documents: RTFEditorKit, StyledDocument, etc..
This means that rtf support only goes as far as Java supports it in their classes.