When we right click on the plplot graph window we will get a popup menu. Is there is a way to add a menu item pdf and clicking on this menu item leads to a pdf file ?
no, there is no easy way other then to improve the wingcc driver itself. But this would be rather straight forward - the wxWidgets driver provides something similar. Just add a menu option, catch the event or set the signal slot and create a new stream, init as pdf device and copy from the current stream. You may ask for a filename, page size, etc. I can't be of any further help, since I have no experience whatsoever with the Windows API.
PS: You could ask the developer mailing list for help, since not many developers read the forums. Maybe one of them can help you.
Can you please provide the developer maliing list url.
https://sourceforge.net/mail/?group_id=2915 where you can subscribe to devel or general list.