If you use Magos Model Editor: (
http://www.hiveworkshop.com/forums/tools-560/war3-model-editor-62876/)
1. Open it
2. Click on "Windows"
3. Click on "MPG Browser"
4. Click on "File"
5. Click on "War3.mpq" if you need units from ReignOfChaos
Click on "War3x.mpq" if you need units from FrozenThrone
6. Click on "Units" (if you want to extract a model of a unit)
7. Choose a unit, for example "Units/Human/Arthas"
8. Open the folder "Arthas"
(Now you see 2 .mdx files (Arthas.mdx and Arthas_Portrait.mdx)
9. Right-Click on Arthas.mdx
10. Click on "Export"
11. Save it somewhere
If you use the WC3Viewer: (
http://www.hiveworkshop.com/forums/tools-560/warcraft-iii-viewer-62878/)
1. Open the Viewer
2. Find the "StructureView-Window" (if it's not there press CTRL+H)
3. Double-Click the path there
4. Double-Click on Units
5. Find Arthas under Human
6. Double-Click on Arthas
7. Right-Click on the Arthas.mdx file
8. Click on "Extract MDX"
9. Save it
Export succesful!!
Use this converter to convert to .mdl:
http://www.hiveworkshop.com/forums/tools-560/mdlx-converter-62991/
Many Greets chilla_killa