Sign with Notarius Digital Signature in Acrobat Pro DC

My professional engineering association is implementing a requirement for digital signatures in electronic reports, and has identified Notarius as the only permissible certifying authority at this time. Notarius have their own signing software ("ConsignO") but it's a ball of hurt and can't handle password-locked PDFs, so there's no way for me to prevent editing of signed files or copying of content. Yes, editing the file invalidates the signature, but some PDF readers (e.g. Preview in MacOS) don't even really acknowledge signing or certification, and even Acrobat itself simply opens the altered PDF without signature, so it might not be immediately obvious to unsophisticated users that the signature was present but is now missing. It's also easy for the content of the files to be copied, up to and including the signature graphic. Bottom line, I'm not sure the digitally signed PDF is any more secure, in the sense of day-to-day functionality, than my old method of a password-protected printable PDF.

So, I'd like to use Acrobat to apply my Notarius digital signature, so I can additionally password protect the document. I've added the Notarius Root Certificate Authority as a trusted certificate, and both "sign documents" and "certify documents" are checked. However, if I try to certify a document, and go through the process of adding a digital ID, the Notarius ID files - and .EPF and an .XCC - are both greyed out. Notarius is listed on Adobe's Approved Trust List Members page (https://helpx.adobe.com/in/acrobat/kb/approved-trust-list1.html#sa_src=web-messaging) so I would have thought that meant the signature should be compatible.

I've spent HOURS with Adobe customer service on this, and they're utterly useless. I'd appreciate any suggestions.