The problem is because in Adobe versions 9, 10 and 11 the validity of the signature is not necessarily verified automatically. Adobe also has to be able to access the Windows Certificate Store. To ensure this is possible, configure Adobe as follows:
Adobe versions 9 and 10: Go to «Edit/Preferences/Security/Advanced Preferences». Select the tab «Windows Integration». The configuration has to be selected as described below. Also check that under «Edit/Preferences/Security» the box «Verify signatures when the document is opened» is selected.
Adobe version 11: In this version the setting for signatures is listed separately and not under «Security». This is how you configure version 11 correctly:
Even after this step is done, Adobe may show you the signature details and confirm that the signature is valid but will ask you to mark this signature as "Trusted".
You may be asked again to trust our signature again for a different AOC PDF certificate as it may be a different Lawyer using a different signature that has signed that second Certificate.
Each signature block will display the name and details of the signing Lawyer.
Below is an example of all signatures showing as valid: