I successfully implemented SumatraPDF as an embedded viewer in a Delphi application.
It's to be launched through a shell command but adding the -plugin parameter makes it child of your form or any container. You can then send keystrokes or use DDE to pilot it.
see the wiki and look for "-plugin".
Sumatra is very fast and redistributable under the GPL conditions, it uses MuPDF as rendering engine, which is a very viable solution.
if you look at the source code of the following Total Commander plugin, you will find how to use it. Just ignore the part of the source that integrates the functionality as a TC plugin
