I don't know how X4 is for sure, but earlier versions of
RoboHelp were Single Document Interfaces, so could only open one
project at a time. That said, it was still possible to open a
second instance of RoboHelp and open a second project, in order to
copy and paste from one project to another. It never allowed you to
open the same project in two separate instances of RoboHelp,
however. This is because RoboHelp is constantly updating the
project as you type. I assume this is still the design in X4. It
seemed to be when I ran a demo version of X5.
John