Sub Test()
Dim pal As New StructPaletteOptions
Dim flt As ExportFilter
pal.NumColors = 16
pal.PaletteType = cdrPaletteOptimized
Set flt = ActiveDocument.ExportBitmap("C:\Temp\img.gif", cdrGIF, , cdrPalettedImage, PaletteOptions:=pal)
flt.Finish
End Sub