\nopdfcompression

\starttext
%     \externalfigure[fig.pdf][page=1]
    \externalfigure[gif.pdf][page=1]
    \externalfigure[gif.pdf][page=2]
    \startoverlay
        {\externalfigure[gif.pdf][page=1]}
        {\externalfigure[gif.pdf][page=2]}
    \stopoverlay
\stoptext