For pumpkins - using the same cutter used to cut cookies, cut fondant. Using a pastry bag filled with orange buttercream and fitted with a round tip, pipe lines in different widths. Place fondant over buttercream. Using a modeling tool, make lines following the piped buttercream. Attach stem with piping gel.
For acorns - cut fondant pieces in the two different colors. Cut the lighter brown to cover the whole cookie and attach to cookie with piping gel. Place the acorn cap on top of the lighter brown with piping gel. With a modeling tool, texture the fat part dark brown cap; not the stem.
For leaves - cut fondant pieces and detail with veiners. Attach to cookie with a thin layer of buttercream or piping gel.