CertViewer 1.2.0 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. The actual developer of the free program is dEajL3kA.
From the developer:
In order to display an X.509 certificate, simply drop a certificate file in the binary (DER) or the Base64-encoded (PEM) format onto the CertViewer window. Alternatively, you can copy a certificate in the PEM format to the clipboard. Last but not least, it is also possible to pass a certificate file to CertViewer via command-line parameter.