clarified NEWS: document_files are officially required since Isabelle2014, but the absence was tolerated as legacy feature;
\documentclass[11pt,a4paper]{article}
\usepackage{isabelle,isabellesym}
% this should be the last package used
\usepackage{pdfsetup}
% urls in roman style, theory text in math-similar italics
\urlstyle{rm}
\isabellestyle{it}
\newcommand{\ganz}{\mathsf{Z}\mkern-7.5mu\mathsf{Z}}
\begin{document}
\title{ZF}
\author{Steven Obua}
\maketitle
%\tableofcontents
\parindent 0pt\parskip 0.5ex
\input{session}
\end{document}