From Delphi you should be able to send Labtalk commands by DDE to Origin, I have used DDE from a program called Testpoint and it works fine. A good idea is to make a template for the worksheet and the graph(s) you want and load the data into these using labtalk commands sent by DDE.
I have not used the PDF-export function, but there exist a export object in Labtalk that should work.
If you like, send me an e-mail and I can send you some examples of the DDE-conversation I am using in my program.