The output from the user depends on what your "Submit" button has been designed to do. By default it will be set to return the data of the form but you can change the properties of the submit button on the form to return the PDF itself.
If you receive a PDF and not the XDP data you will need to use the importData and exportData functions to get data in and out of the form. A few more steps are required to work with PDF's when compared to XDP.
If you want to use a DigSig on your form then you will need to submit a PDF.