I have submitted two applications with different descriptions but which refer to the same concept. E.g. one application describes a substance in an oral pill form and the other application describes the same substance in an injectable form. I want to submit a PCT and merge the two applications claiming priority from both of them. Is that possible?
Yes, it is possible. Art. 8(1) PCT:
The international application may contain a declaration, as prescribed in the Regulations, claiming the priority of one or more earlier applications filed in or for any country party to the Paris Convention for the Protection of Industrial Property.
And the fact that the two applications relate to the same concept has no bearing on priority or the content of another application.