\documentclass[letterpaper]{article}
%\VignetteIndexEntry{Censored Quantile Regression}
%\VignettePackage{quantreg}

\usepackage{pdfpages}

\begin{document}

\newread\PDFtoInclude
\openin\PDFtoInclude=crq0.pdf
\ifeof\PDFtoInclude
\typeout{No file crq0.pdf}
\else
\includepdf[fitpaper=true,pages=-]{crq0.pdf}
\fi

\end{document}
