\documentclass[a4paper,10pt]{scrartcl}

\usepackage{helvet}
\usepackage{lipsum}
\usepackage{titling}
\usepackage[]{fancyhdr}
\usepackage{xcolor}
\usepackage{lastpage}
\usepackage[top=2.5cm,bottom=2.5cm,left=2.5cm,right=2.5cm,footskip=1.5cm,headsep=0.8cm,headheight=1cm]{geometry}

% \usepackage{scrpage2}
\renewcommand{\headruleskip}{0.2cm}
\renewcommand{\footruleskip}{0.5cm}
\renewcommand{\headrulewidth}{0.0pt}
\renewcommand{\footrulewidth}{0.0pt}


\author{Miriam Brosi}
\title{Document Title}

\begin{document}
% \pagestyle{scrheadings}
\pagestyle{fancy}
\fancyhf{}
% \fancyhead[LE]{\nouppercase{\rightmark\hfill\leftmark}}
% \fancyhead[RO]{\nouppercase{\leftmark\hfill\rightmark}}
% \fancyfoot[LE,RO]{\hfill\thepage\hfill}
%\fancyhead[R]{\nouppercase{\leftmark}}
\fancyhead[R]{\color{gray}Page \thepage\ of \pageref{LastPage}}
\fancyhead[L]{\color{gray}\nouppercase{\thetitle}}
\fancyfoot[R]{\color{gray}\theauthor}

\noindent
{\fontsize{16}{16}\selectfont \thetitle}

\section{First Section}

\lipsum[1]

\subsection{First Subsection}

\lipsum[1]

\pagebreak

\section{something}

\lipsum
\lipsum

\end{document}