If you want to validate a StepOver signature in Adobe Reader/Acrobat you would normally see that the identity of the signer is unknown. This is because a "self-signed" certificate is used for the signature, which is not trusted by Adobe Reader/ Acrobat by default. To change that, you have to install the appropriate Root-Certificate.
Therer are 2 certificates:
Download certificate here:
Installation Guidelines for Adobe Reader / Acrobat