pdfconfig.tex

\documentclass[12pt]{scrartcl}
\usepackage{pgfkeys}
\begin{document}

\newcommand\pdfconfig

\pgfkeys
{
  /includepdffiles/.is family, /includepdffiles,
  % Calling the keys so that the macros are defined.
  default/.style =
  {
    pdfconfigfilename,
  },
  pdfconfigfilename/.default = {},
  pdfconfigfilename/.estore in = \pdfconfigfilename,
}

\NewDocumentCommand{\IncludePDFFiles}{O{}}
{
  \pgfkeys{/includepdffiles, default, #1}%
  \typeout{\pdfconfigfilename}
}

\IncludePDFFiles[pdfconfigfilename=FOO]

\end{document}

%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End: