Save the certificate to a file (from -----BEGIN CERTIFICATE----- to -----END CERTIFICATE----- inclusive) as mekkis_sign.cert .
Open Acrobat Reader.
Go to Edit->Preferences
Click "Signatures" on the left panel.
In the group named "Identities & Trusted Certificates", click More...
On the left pane, choose "Trusted Certificates"
Click "Import", browse, and import mekkis_sign.cert
Click on Mekkis, on the upper panel. Mekkis should appear on the lower panel. Select Mekkis and import.