The primary drawback of using self-signed certificates is that they are only useful if you exchange documents with those who know you personally and are confident that you are the actual originator of the document.
By using self-signed certificates, there is no third party that validates the authenticity of your certificate.
If you want digital signatures that you create in Office 2013 to be compatible with Office 2003 and earlier versions, you can configure the Group Policy setting, Legacy format signatures, and set it to Enabled.
Each person who receives your signed document must manually decide whether to trust your certificate.
For larger organizations, two primary methods for obtaining digital certificates are available: certificates that are created by using an organization or corporation PKI and commercial certificates.
Digital certificates are verifiers of identity that are issued by a trusted third party, which is known as a certification authority (CA).
This works similarly to the use of printed identity documents.