documentclass{article}
begin{document}
   section{Doc A}
   input{docA}
   section{Conclusions}
   Very good.
end{document}

section{Hello}
This should actually be a subsection.
subsection{World}
And that one is a subsubsction.

documentclass{article}
begin{document}
   section{Doc A}
   {
letsectionsubsection
letsubsectionsubsubsection
input{docA}
}
   section{Conclusions}
   Very good.
end{document}