Cannot place a signature on a PDF document

I just encountered an issue with a specific PDF issued to me by a vendor. I am normally able to "place signature" on any PDF document. This one however, only allows me to place a certificate-based digital signature. How can I go about simply placing my signature on the document?

I also do not have my serial number as I purchased the software as an option through Lenovo. They don't have my serial numbers and neither does Adobe evidently. Not the greatest customer service experience I've had.