\setcounter{secnumdepth}{3}
\setcounter{tocdepth}{3}

\usepackage[noindentafter]{titlesec}

% paragraphs sehen aus wie subsubsubsections
\titleformat{\paragraph}[hang]{\bf}{\thetitle\quad}{0pt}{}
\titlespacing{\paragraph}{0pt}{1em}{0.5em}

% subparagraphs sehen aus wie vorher paragraphs
\titleformat{\subparagraph}[runin]{\bf}{}{0.5em}{}
\titlespacing{\subparagraph}{0pt}{1em}{1em}