The PDF is an XFA form created in LiveCycle and would not be supported by Fill & Sign.
Digital Signatures as far as I can tell *should* work but I also see the options grayed out when I open the PDF in Acrobat Pro DC (I do not know why).
I moved the thread into the LiveCycle Digital Signatures forum (hopefully that is the right forum) and someone here should be able to help.
Since the LiveCycle form did not have "digital signature fields" added when it was designed the existing signature placeholders (they are not form fields) will not be able to be signed regardless of the document security setting for "signing" since the "Modify" is not allowed.
Since you are a consumer of this form and not the author I won't try to go into what should happen to make the form more usable - you should probably fill out the form in Acrobat or Reader, print and then sign with ink on paper. Once signed you could mail or scan the form to email.
So far, this has been the most accurate and truthful answer in all the forums reviewed.