\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}