Hi!
This is Autodesk.Revit.ApplicationServices.Application class method. It is located in RevitAPI.dll
This method is not static, you should first of all get Application object, for example from command data:
public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
...
var app = commandData.Application.Application;
or just document
var uiapp = commandData.Application;
var uidoc = uiapp.ActiveUIDocument;
var doc = uidoc.Document;
var app = doc.Application;
And only then call this method
Dear Philippe,
Thank you for your query.
You can read this StackOverflow thread which explains how to proceed:
https://stackoverflow.com/questions/4438900/how-to-view-dll-functions
There are only a handful of Revit API .NET assemblies to explore, so it should be a matter of minutes.
I hope this helps.
Once you have answered your question, you can share the result with us, if you think it is useful.
Thank you!
Best regards,
Jeremy