Pick the surname you wish to use, then in your PAF go to the oldest person in that line. Then go to the top left of your PAF screen and choose File, then Export. In the File Export window, choose Other GEDCOM 5.5. In the Selected Individuals section, choose Partial. On the right of that box, press Select. The Select Individuals window should pop up that will show your oldest person for that surname selected. In the Relationship Filter box, choose All Descendants Related. Then press the Select button at the bottom of the window. Your screen will flash and then on the far right you should have a total for all those selected. Then press OK at the bottom of the window. You will be asked to give the GEDCOM a name. Lots of *churning* will take place and then your *specialized* GEDCOM will be generated.I hope this helps you. Let me know if you have any other questions about this procedure.