If your web host is running Activestate Perl and have Microsoft Word installed, you could create the file using OLE. See Win32::OLE
We used that technique to create Excel files. Now we might have used Spreadsheet::WriteExcel instead.

It's sure nice to have a perl-only solution, but if you already have heavily loaded Word documents and templates, it might be easier to use OLE just to fill in a few things, rather than creating a RTF from scratch.