If the PDF file does not successfully validate then a warning message will appear. A certificate will successfully validate only if it has the appropriate metadata that anchor it on the Bitcoin’s blockchain. If not, for example, if the physical copy was scanned and provided to the validator, it will fail to validate since it will be missing the necessary metadata to match it to the blockchain entry.
Please note that an unsuccessful file validation does not necessarily mean that the document is not authentic. It may be the case that the specific PDF is not the original one that was generated by Block.co and published on the blockchain.
In this case, we suggest contacting Mr. Alexis Nicolaou (email@example.com) for further information regarding that certificate.