\documentclass[a4paper, 12pt]{article}
\usepackage{ngerman}
\usepackage[utf8]{inputenc}
\usepackage{dsfont}
\usepackage{wasysym}
\usepackage{eurosym}
\DeclareUnicodeCharacter{20AC}{\euro{}}

\pagestyle{plain}
\oddsidemargin0cm
\evensidemargin0cm
\textwidth16cm
\topmargin0cm
\headheight0cm
\headsep0cm
\textheight24cm
\parskip4pt
\parindent0pt
\baselineskip18pt

\def\da{\left|\begin{array}{ccccc}}
\def\de{\end{array}\right|}
\def\Lra{\Leftrightarrow}
\def\lra{\leftrightarrow}
\def\ma{\left(\begin{array}{ccccc}}
\def\me{\end{array}\right)}
\def\ovl{\overline}
\def\Ra{\Rightarrow}
\def\rlh{\rightleftharpoons}
\def\va{\left(\begin{array}{c}}
\def\ve{\end{array}\right)}
\def\x{\times}

\renewcommand{\baselinestretch}{1,5}

\begin{document}
\noindent
  Hier mit dem eigentlichen Text beginnen.
\end{document}