# Checking the validity of a signature

By default, signatures are validated when you open a PDF. An icon appears in the signature field on the document page to indicate the signature status. Further details about the status appear in the Signatures panel and in the Signature Properties dialog box.

Third-party signature handlers may provide alternate methods of validating signatures. Check the documentation included with your third-party digital ID.

Important: To ensure that signatures are validated when you open a PDF and that all verification details appear with the signature, set your verification preferences in advance (see Set signature verification preferences).

- The digital signature icon along with the name of the field in the Signatures panel indicate the presence of an unsigned signature field.

- The blue ribbon icon indicates that the PDF is certified—that is, it contains a valid certifying signature. (Certifying signatures can be visible or invisible.)

- The check mark icon indicates that the signature is valid.

- The red x icon indicates that the signature is invalid.

- The caution triangle icon indicates that the document was modified after the signature was added.

- The question mark icon indicates that the signature couldn’t be validated because the signer’s certificate isn’t in your list of trusted identities.

If the signature status is unknown or unverified, or if the document was modified after it was signed, validate the signature manually to determine the problem’s cause and possible solution. If the signature status is invalid (indicated by the red x icon), contact the signer about the problem.