See this PDF for example in most PDF viewers https://royalegroupnyc.com/wp-content/uploads/seating_areas/sample_pdf.pdf
All radio buttons are unselected until a user picks an option, then they are forced to pick an option. the SfPdfViewer should replicate this functionality.
I have a bunch of forms that have radio button fields and one at random is always selected as the default value. I have found ways to force which one is selected first by modifying the PDF's. However, this is forcing me to add an N/A option to every radio button selection in my PDF's, which adds a bunch of clutter.
TLDR; All radio button options should be unselected until a user picks an option.