Hello Mc, I'm not exactly sure what you are doing, but you can export the doodads files in the editor under the file in OE, or export the .doo file using a mpq editor.
To clarify some things, to make these new doodads appear, you will also need their object data which is the war3map.w3d file. the d file from the original map and the other map must be combined if you wish to keep your map's doodads in tact. The only tools that i recall capable of doing this in a quick and efficient manner is JNGP or GMSI.