sample_section.tex

% This is a sample section file to demonstrate how these should be written

% See Overleaf multi-file LaTeX project guide here: 
% https://www.overleaf.com/learn/latex/Multi-file_LaTeX_projects

\documentclass[../main.tex]{subfiles}

\begin{document}

\chapter{This is a test}
    
\textbf{Hello, world!}

\end{document}