This policy setting lets you specify whether or not Office 2013 checks the XAdES portions of a digital signature, if present, ...

This policy setting  lets you  specify whether or not Office 2013 checks the XAdES portions of a digital signature, if present, when validating a digital signature for a document.  If you enable this policy setting, Office 2013 checks the XAdES portions of a digital signature when validating it.If you disable or do not configure this policy setting, Office 2013 only validates XML-DSig and XAdES-BES portions of a digital signature.