\documentclass{article}
\usepackage[greek]{babel}
\usepackage[unicode,bookmarksnumbered]{hyperref}

\begin{document}
\section{%
  \greeknumeral{6},
  \greeknumeral{97},
  \greeknumeral{345},
  \greeknumeral{1234},
  \greeknumeral{12345},
  \greeknumeral{123456}%
}
\appendix
\section{Appendix}
\end{document}
