https://www.mydomain.com/myJavaServlet

https://www.mydomain.com/myFile.pdf#nameddest=Chapter3

https://www.mydomain.com/myJavaServlet

req.getRequestDispatcher("https://www.mydomain.com/myFile.pdf#nameddest=Chapter3").forward(req, res);

String url = "https://www.mydomain.com/myFile.pdf";
RequestDispatcher requestDispatcher = getServletContext().getRequestDispatcher(url);
requestDispatcher.forward(req, res);

String url = "/WEB-INF/myFile.pdf";

RequestDispatcher requestDispatcher = req.getRequestDispatcher(url);