I found it out by myself:
Include https://github.com/mono/monodevelop/tree/master/main/src/addins/MacPlatform/MacInterop to your project.
use this code
ApplicationEvents.OpenDocuments+= delegate (object sender, ApplicationDocumentEventArgs e) { if (e.Documents != null && e.Documents.Count > 0) { // e.Documents holds the files } e.Handled = true; };