A xfaForm variable is really just a pointer to a XDP in the repository and a render service that renders the XDP into a PDF when presented in WorkSpace.
In the process the xfaForm variable contains only the data from the PDF but not the PDF itself.
So when you say you want to convert the xfaForm variable into a document variable, I'm assuming you want to store the PDF representation of the xfaForm variable in that document variable right?
Since the document variable is an Adobe data type and can really contain anything, you could store the value of the xfaForm variable in the document but you would only get the xml data.
If you want the PDF you'll need to use LiveCycle form to convert the XDP into a PDF, merge the data from the xfaForm variable and store the resulted in the document variable.
Just to clarify Jasmin:
You'll need either LiveCycle Forms (not form) component, the Render operation, or Form Data Integration component, ImportData operation.
Can I use the renderPDFForm Service to convert the xfa form to PDF without render it to workspace?
I tried to use it to convert the form to PDF but not sure what should I input for the URL Options?
Can I include attachments in the PDF as well?
Yes, renderPDFForm (part of the Forms Service) is for merging data and template and getting a PDF. With the 8.2 version the URL settings are used to point to the template location. It uses a URI format - i.e if the template was in your myForms folder in the repository your settings would be:
Form to Render: /myForms/mytemplate.xdp
Content Root URI: repository://