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This warning means that there is a problem with the digital signature or the certificate that was used to sign the workbook. A digital signature is a way to verify the authenticity and integrity of a workbook, and a certificate is a way to identify the signer and the issuer of the signature.
There are some possible reasons why you may see this warning, such as:
• The digital signature or the certificate has expired or been revoked. This means that the signature or the certificate is no longer valid or trusted, and you may need to update or renew them.
• The digital signature or the certificate is not recognized or trusted by your device or application. This means that the signature or the certificate is from an unknown or untrusted source, and you may need to add them to your trusted list or verify their identity.
• The workbook has been modified or corrupted after it was signed. This means that the signature or the certificate does not match the current content or format of the workbook, and you may need to check if the workbook has been altered or damaged.
To fix this issue, you can try the following steps:
• View the details of the digital signature or the certificate, and see if they are valid, invalid, or recoverable. To do this, you can open the workbook, click File > Info >View Signatures, and then click the down arrow on the signature name and click Signature Details.
• Update or renew the digital signature or the certificate, if they are expired or revoked. To do this, you may need to contact the signer or the issuer of the signature or the certificate and ask them to provide you with a new or valid signature or certificate.
• Add or verify the digital signature or the certificate, if they are not recognized or trusted by your device or application. To do this, you can open the Signature Details dialogue box and then click View Certificate. Then, you can check the certificate status, and see if you need to install the certificate, trust the certificate, or contact the certificate issuer.
• Check or repair the workbook, if it has been modified or corrupted after it was signed. To do this, you can compare the workbook with the original or backup version, and see if there are any changes or errors. You can also use the Open and Repair feature in Excel to try to fix the workbook. To use this feature, you can go to File > Open, and then click the arrow next to the Open button and click Open and Repair.
Note: You might need to translate the page content in the link shared below.
From <https: support.microsoft.com/office/view-digital-signature-and-certificate-details-76ba00cb-1e58-42aa-8717-0caee76bb3cf="">
https://support.microsoft.com/office/add-or-remove-a-digital-signature-for-microsoft-365-files-70d26dc9-be10-46f1-8efa-719c8b3f1a2d
If you have any further questions or need additional assistance, please feel free to ask. I'm here to help!
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Ajibola.
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