

\documentclass[twocolumn,a4paper]{article}
\usepackage[margin=2cm]{geometry}
\usepackage{zebra-goodies}
\usepackage{lipsum}
\pagestyle{empty}
\begin{document}
\section{Demo name\comment{revise the name}}
\lipsum[1] \todo[alice]{revise the introduction}

\lipsum[2] \note[bob]{add a reference here}
\lipsum[3] \fixed[carol]{looks good now}
\lipsum[4] \todo[dave]{needs more data}

\lipsum[5] \placeholder[eve]{insert figure}

\lipsum[6] \note[frank]{check the numbers}

\lipsum[7] \comment[tom]{is it you, jerry?}

\lipsum[8] \fixed[heidi]{typo corrected}

You can place \todo[judy]{summarise the findings} anywhere.
\lipsum[9][10-11]
\end{document}
