\documentclass[a4paper, 13pt]{article}

% Packages
\usepackage[a4paper, inner=2.5cm, outer=2.5cm, top=2.5cm, bottom=2cm, bindingoffset=0cm]{geometry}
\usepackage{amsmath,amsthm,amssymb,amsfonts}
\usepackage{graphicx}
\usepackage[colorlinks=true, allcolors=blue]{hyperref}
\usepackage{fontspec,xunicode,xltxtra}
\usepackage{afterpage}
\usepackage{sectsty}
\usepackage{tikz,float}
\usepackage{svg,lipsum}
\usepackage{eso-pic}
\usepackage{fancyhdr}

% Font
\setmainfont{"[font.ttf]"}
\sectionfont{\fontsize{20}{15}\selectfont}

% GERMAN
\usepackage[ngerman=ngerman-x-latest]{hyphsubst}
\usepackage[ngerman]{babel}

% Figures
\graphicspath{{figures/}}

% Header & footer
\renewcommand{\footrulewidth}{0pt}
\pagestyle{fancy}
\fancyheadoffset{2.5cm}
\fancyfootoffset{2.5cm}
\fancyhf{}
\fancyhead[L]{\hspace*{1cm}\huge{\leftmark}}
%\fancyhead[R]{Abitur 2021}
\lfoot{\hspace*{1cm}\huge{\thepage}}

% Custom title command for header
\renewcommand{\title}[1]{
	\par\refstepcounter{section}
	\sectionmark{#1}
	\addcontentsline{toc}{section}{\protect\numberline{\thesection}#1}
}

\begin{document}

\title{ABI Zeitung 2021}
\author{des RBS Ulm}

% Updated: https://tex.stackexchange.com/a/7657
% Import all tex files from a directory
\def\app@exe{\immediate\write18}
\def\inputall#1{
    \app@exe{cat #1/*.tex > #1/files.tmp}
    \InputIfFileExists{#1/files.tmp}{}{}
    \AtEndDocument{\app@exe{rm -f #1/files.tmp}}}

\def\part#1{\input{parts/#1.tex}\newpage}
\def\student{\input{parts/studenttemplate.tex}}

%\maketitle

\part{titlepage}
\part{tableofcontents}
\part{introduction}
\part{classphoto}
\part{questionnaire}
\part{teacherprofiles}
\part{teacherranking}
\part{secrets}
\part{classoverview}
\part{studentprofiles}
\part{studentranking}
\part{citations}
\part{photos}
\part{trips}
\part{courseoverview}
\part{committeeoverview}
\part{conclusion}
\part{advertisements}
\part{imprint}

\end{document}