You can add those back in once you've determined the solution. The following code works for me: `Remove[f, n, h];
n = 4;
h = 1/10000;
f[x_] := 1/10 Sin[3 x] Exp[-x] x;
ddddf = 1/h^n Sum[(-1)^(k + n) Binomial[n, k] f[x + k h], {k, 0, n}];
Plot[ddddf, {x, 0, 5}, PlotRange -> All, WorkingPrecision -> 20]`.