Can't validate digital signature

[Annemarie Rom-Weisenbach]

Hello,

About 2 weeks ago, various digital signatures on our PDFs are showing as invalid. I don't remember seeing this before. The same signatures are showing as valid with Acrobat Reader.

I have tried clicking on the signature itself, and also using the Signature pane on the left, to Validate the signatures.

For one signature, the Validate Signature button is active but clicking it seems to do nothing. There is no error message but nothing happens/changes.

For another signature, the Validate Signature button (as well as all the other buttons in that dialog box) is greyed out and not active.

I am running Nitro Pro v 13.58.0.1180.

Please help. These are important official govt documents.