We have seen in eID Easy that sometimes Adobe Acrobat might show that qualified timestamp from EU TSL validity is unknown. This can happen when new CA certificates are issued and these are not yet picked up by the Adobe Acrobat and you can force it for a manual update of trusted lists from the Acrobat Preferences > Trust Manager > EUTL > Update Now.
One of the popular QTSA-s that might have this issue is Baltstamp in August/September 2024 because their new CA was added to European trusted lists in July. Adobe Acrobat updates EU TSL-s automatically once a month. If Adobe published their new list in August then after publishing new trust lists would take a month to be automatically uploaded everywhere.
If Adobe trusted lists are not yet updated then signature verification panel shows "Signature validity is unknown":
After updating the Adobe trusted lists manually the verification will succeed:
You can force it for a manual update of trusted lists from the Acrobat Preferences > Trust Manager > EUTL > Update Now. The settings view for Updating the Trusted lists in Trust Manager is this:
