Ok, if you're talking about converting from FAA to EASA.. EASA log PIC differently to the FAA.
Under the FAA system you can log PIC without actually being the legal PIC.
Under EASA, you can only log PIC if you were the legal PIC.
So for an instrument training flight with your instructor you can log FAA PIC and dual, but EASA would not recognise this as PIC because you weren't the legal PIC. You can log dual, or PIC but not both (unless it's pocus!)