Step 2: Click on the Signature Panel button, which will be on the right of the error.

Step 3: Click on the Validate all link. It will prompt the message to validate all signatures depending on the settings. 

Step 4: Click OK to validate all the signatures. Once all signatures are validated it will show a success message depending on the settings.

Step 5: If the signatures are successfully validated Adobe Reader will show the message Signed and all signatures are valid. If that is the case, you can skip the next steps.

Step 6: If the At least one signature has problems error is still visible, select the signature which has the problem and right click on it. It will display a pull-down menu. Here, select Show Signature Properties in the menu and the Signature Properties window is shown.

Step 7:  Click on the Show Certificate button, and a Certificate Viewer window will open from where you can see the details of the certificate. 

Step 8: From the Certificate Viewer window, click on the Trust tab, and you can now see the Trust settings. Here, you will see the This Certificate is not trusted message. 

Step 9: Click Add to Trusted Identities and when Adobe Reader asks if you are sure you want to add it click OK.

Step 10: Now it will display Import Contact Setting window. Select Use this certificate as a trusted root checkbox and click on OK button to import contact settings into your system.

Step 11: Now the signature is validated and it will display Signature is VALID, signed by message in Signature Properties window which is opened in Step 6.

Step 12: Click on Close button to close Signature Properties window.