Click on the EXPORT button in the upper left on the main PAF screen (the little floppy disk icon with the arrow going out).The EXPORT dialog screen will appear.
The first thing you want to do is click the "Partial" radio button near the bottom left of the EXPORT dialog screen.You can also select the destination of your exported file (left half of dialog screen); and you can check what you want to include in your file (right half of dialog screen).If you don't know what genealogy program your cousin has, or if your cousin has a program other than PAF 5.2, then click the bottom radio button (Other GEDCOM 5.5).
Once you click "Partial" then click the "Select" button (bottom right of screen).You are presented with an index from which to select.Find your cousin (for example) and pull down the selection menu (near bottom left of screen); choose "Ancestors" and then click on the "Select" button. You are now presented with a little selection screen; how many generations do you want?Do you want all the siblings of your ancestors? Do you want their spouses?
Now find and highlight your grandfather (the one who is also your cousin's grandfather); pull down the selection menu again and choose "Descendants" and then click the "Select" button.You are again presented with a little selection window, but the only blank to fill in is how many generations of your grandfather's descendants do you want.
Now click on the "OK" button (lower left corner of screen)and you are back to the Export Dialog Screen.Click the "Export" button (lower left corner of screen) and you will be prompted to give your new GEDCOM file a name (here you can also browse until you find the right folder to put the new file in, before you name it).