Trust and Authenticity

Signing a PDF file with a digital signature requires a bit of background knowledge. When the PDF reader tries to decide if a signature is valid then it looks at the certificate used to sign the document. A signature can make sure that nobody tampered with the content of the document since it was signed.

In addition, the signature is used to determine if you trust the content. Trust is based on the certificate behind the signature. Certificate trust depends on the issuer of the certificate. The reader will trust a certificate if you have told it to trust the issuer of that particular certificate.

By default the Adobe Reader only trust certificates issued by Adobe or one of their partners. This means that it will show a certificate warning if the certificate wasn’t issues by one of these authorities. Microsoft Windows also uses certificates for validating software vendors and content providers. You can configure your Adobe Reader to trust these issuers in addition to the Adobe partners. This extends the range of certificates that will show as valid certificates when you receive or create a signed document.

You can also get a certificate that doesn’t stem from one of the trusted providers. Then it is up to you to have your document recipients add that certificate to their list of trusted certificates. If they do that, then your signed documents will show as validated and trusted if they are received in their original state.