Sign digital field in sign fields in adobat acrobat form

Hello:

I have Adobe Acrobat Pro DC. I have created a form and I need that two persons sign it using digital sign.

When I choose mails of the people must sign, digital sign field doesn't appears and not can be included.

Only appears electronic sign and sign block.

Anybody knows why?

In picture attached you can see the fileds that only are available (red square)

How can I use digital sign field when i choose people must certificate the pdf file?

Thanks in advance.