documentclass{article}
begin{document}
This document describes subject "A".
begin{figure}
caption{First Figure}label{fig:1}
end{figure}
See Figure~ref{fig:1}.
end{document}

documentclass{article}
begin{document}
This document describes subject "B".
begin{figure}
caption{First Figure}label{fig:1}
end{figure}
See Figure~ref{fig:1}.
end{document}

documentclass{article}
begin{document}
This document describes subject "C".
begin{figure}
caption{First Figure}label{fig:1}
end{figure}
See Figure~ref{fig:1}.
end{document}

documentclass{article}
begin{document}
This document has a description of all subjects.
section{Chapter 1}
include{Document-A.tex}
section{Chapter 2}
include{Document-B.tex}
section{Chapter 3}
include{Document-C.tex}
end{document}