As a Windows user, follow the instructions below in order to trust the signature.

Go in the Edit menu of your Acrobat Reader to Preferences. The screen below appears.

Click the Category Security and open the Advanced Preferences window. The screen below will appear:

Select the tab Windows Integration and select the first and the third frame as shown above. Click OK to confirm.

When you reopen the signed PDF document, the signature is validated.

In some cases there could still be a problem with the validation of the signature, caused by problems in checking the revocation list.

Since the revocation list is retrieved from an external source (http://crl.globalsign.net/PersonalSignClass3.crl), it might be blocked for instance by a proxy server.

The revocation list checking can be skipped by un-checking the following parameter in the advanced security settings: