\def\thumbnailpdf#1{%
    \pdfximage{#1}%
    \newcount\pagenum%
    \newcount\totalpages%
    \pagenum=0%
    \totalpages=\pdflastximagepages%
    \loop%
        \hbox to \hsize{%
            \advance\hsize by -\columnsep%
            \divide\hsize by 2%
            \global\advance\pagenum by 1%
            \ifnum\pagenum<\totalpages%
                \pdfximage width \hsize page \pagenum {#1}%
                \pdfrefximage\pdflastximage%
            \fi%
            \hfil%
            \global\advance\pagenum by 1%
             \ifnum\pagenum<\totalpages%
                \pdfximage width \hsize page \pagenum {#1}%
                \pdfrefximage\pdflastximage%
            \fi%
        }%
        \vskip \columnsep plus 1000pt minus 0pt%
    \ifnum\pagenum<\totalpages\repeat%
    \vskip \columnsep plus 2fil minus 0pt%
}