If you see the Validate tool under Protect grayed out as shown below:
Please check to make sure the document has digital signatures on the file for our software to check validation.
If you are using ink signatures, the feature will not be valid as it must be a digital signature with valid security
If you deployed the software with an MST file, please also make sure that the following option is not checked:
Please also make sure that features which require internet connection is not disabled: