\documentclass[a4paper]{article}

\usepackage{candidature}

\addbibresource{bib/hdr_noverlan.bib}
\addbibresource{bib/hdr_verlan.bib}
\addbibresource{bib/insdel.bib}
\addbibresource{bib/pn.bib}
\addbibresource{bib/psystems.bib}

\begin{document}

\section{Dummy}

\cite{Korec}

Hello World
\end{document}