Are signatures valid after the certificate has expired?

Yes, as long as long-term validation (LTV) is enabled.

Certificates have an expiration date which is set by the issuing authority. For example, certificates issued by I.CA are valid for a year.

However, there is no need to worry that your signature will become invalid after the certificate validity period has ended. As long as LTV is enabled (in Circularo, it is always enabled by default), the signature will be valid indefinitely. This can be easily verified in Adobe Acrobat or other verification tools available online.

In the edge cases where LTV is disabled (in Circularo, this can be done upon request from the organization), the signature validity period will be the same as the certificate validity period.