Hello Bruno,

here is a sample how I'm adding a .dot file to word and call a VBA macro in
it.
Maybe you find it usefull.

// our word AddIn
Word.AddIn addIn = wordApp.AddIns.Add( "C:\\X4UTools.dot", ref _Missing);

// call our Macro to set the button image
Type wordType = wordApp.GetType();
object[] args = { "UpdateToolBar", "XConnect", "XMail", assemblyPath +
"X4UButtonPicture.bmp", assemblyPath + "X4UButtonMask.bmp" };

wordType.InvokeMember("Run", BindingFlags.Public | BindingFlags.NonPublic |
BindingFlags.InvokeMethod, null, wordApp, args);    

// Remove Addin
addIn.Delete();

// Cleanup
if (wordApp != null) Marshal.ReleaseComObject(wordApp);

This should be a starting point.

Hope this helps,