This post explains how to make sections invisible. Because I want to get rid of the numbers in the headers and the ToC I would like to do the same with addsec. But I cannot get this to work.
\documentclass{scrbook}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage{lipsum}
\newcommand\invisibleaddsec[1]{%
\refstepcounter{addsec}%
\addcontentsline{toc}{addsec}{\protect\numberline{\theaddsec}#1}%
\addsecmark{#1}}
\begin{document}
\invisibleaddsec{Header}
\lipsum
\end{document}
gets an error message.