A view things we would need to know before i can give you a proper anwser
Option 1: user is filling the PDF Form in LiveCycle Workspace
In this case you can use the assign task component in the process design which will allow you to retrieve the user filled out data into a variable containing the XDP result (formated XML)
Option 2: user fills a PDF form and sends data via Submit button as XML back to the LiveCycle server
Standard submit buttons designed on PDF forms allow you to send the data XML formated out of the PDF form. In this matter your process would be for example enabled to retrieve a email with the XML data attached. In the process you assign the process data into a XML process variable which you defined.
option 3: user fills the PDF form and sends the filled out form back
The process is picking up the PDF from a watched network folder or email, assign it to a process variable with the type document. In the process you seperate the data from the PDF with the FORM server component. Make sure you have the FORM server installed, then you should have the services from the FORM server in your component libary.
Which way you want to go ?
I am talking about 3rd senario, where we create one process on workbench, and pass filled pdf as input and then output of process is xml file.
What is the process name here (Like renderPDF process) which extract data from pdf.
Try ExportData or ProcessFormSubmission service.
Hope it helps!