http://btcmixer2e3pkn64eb5m65un5nypat4mje27er4ymltzshkmujmxlmyd.onion/help/trade/trusting-pdf-signing-certificate
It is "Self-Signed" and not rubber stamped by a well known trusted
Certificate Authority like GlobalSign, DigiCert, GoDaddy or Verisign
because in order to get such a Certificate would require us to submit
our own personal details to such a third-party, which is not going
to happen. You have the option to choose to trust Anonymixer's Self-Signed
Certificate which Signs PDF documents, in a similar way that you would
trust a PGP...