The PFD  is the only screen that does not expand to a larger screen in the PMDG B737NG with the P3DV4...It did expand when I was using FSX....So, why not now?

You can enable the PF PFD via the FMC option menu; it's disabled by default because its been known to cause system crashes on some long-haul flights. 

I couldn't find any option in the FMC to enable the choice of expanding the PFD. I looked under both the aircraft and display options...Can you help me on this. Thanks

I found it,to enable the PFD popup.  Again thanks for your help.