\section{In the subfile}
And here is the subfile, with the included figure.


\begin{figure}[htb]
  \centering
  \psfrag{F}{$\Fset$}
  \psfrag{G}{$\Gset$}
  \psfrag{f}{$f$}
  \psfrag{f-inv}{$f^{-1}$}
  \pdfrackincludegraphics[width=.6\linewidth]{FfG}
  \caption{The figure in the sub-file}
  \label{fig:indoc}
\end{figure}