Revit is based on Windows. You can copy/paste from program to program regardless of the program in Windows.
But for some weird reason you cannot copy/paste from two different sessions of Revit, only from within the same session. When working on a memory intensive project, it is better to have another session of Revit running instead of the primary in case of a program crash and lose both projects.
Why?
It works for AutoCAD.
While I know Revit is NOT Autocad.....Revit is based on Windows and we cannot do this simple task.
So....Why? Please fix.