MWE

\documentclass[a4paper]{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[italian]{babel}
\usepackage[runs=2]{auto-pst-pdf}

\makeatletter
\ifpdf
\expandafter\@firstofone
\else
\expandafter\@gobble
\fi
{\usepackage{hyperref}}
\makeatother

\begin{document}
    \include{chap1}
    \chapter{Second chapter}
    \ref{first}
\end{document}


%%% file chap1.tex %%%

\chapter{First chapter}\label{first}

Text