First take a look at Vector Graphics Formats. This is an easy way to make Voronoi diagram
vd = ListDensityPlot[pts = RandomReal[1, {150, 3}],
InterpolationOrder -> 0, ColorFunction -> (White &), Frame -> False,
BoundaryStyle -> Black, Epilog -> {Red, Point[pts[[All, 1 ;; 2]]]}]

These are some vector formats in Mathematica:
Export["tst." <> #, vd] & /@ {"svg", "wmf", "emf", "eps", "pdf", "dxf"}
{"tst.svg", "tst.wmf", "tst.emf", "tst.eps", "tst.pdf", "tst.dxf"}
For .PDF you may have to look into option "AllowRasterization"->False
see details here.