Certify options not active ("Use a Certificate" tool)

Hello Community,

After an unhelpful and rude chat with Adobe support saying that this is a free tool and I do not get support from them , I am turning to you.

I have tried to follow on my own this guide:

https://helpx.adobe.com/in/acrobat/using/certificate-based-signatures.html

BUT, the Certify options are not active for me (grayed out)

Q1) How can we enable/use those Certify (both with visible and invisible signatures)?

it is not mentioned in the guide what the requirements or configuration is

And, I did search on the community or online before... so:

Yes, this does happen on all PDFs (none are previously signed or certified; for example, I just print a page as PDF and try to Certify it)

Yes, I do have the latest version (went to help / check for updates)

THANK YOU FOR YOUR HELP !