Solutions to fix Can’t verify signature Installation Error in Office 365/2021/2019
Several reasons for this Error Message Can’t verify signature :
The signature has been tampered with:
If the digital signature has been altered in any way, the verification process will fail. This could happen if the file has been modified after it was signed or if someone tried to alter the signature itself.
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The digital certificate used to create the signature may have expired, been revoked, or was not issued by a trusted certificate authority.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.