Solutions to fix Can’t verify signature Installation Error in Office 365/2021/2019
When you see the error message “Can’t verify signature,” it means that the digital signature on the file or document you are attempting to verify cannot be confirm as authentic or valid.
The digital certificate used to sign the file is invalid:
The digital certificate used to create the signature may have expired, been revoked, or was not issued by a trusted certificate authority. This would make the signature invalid and unverifiable.