Converting .cer to .pem errors

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http://serverfault.com – I realize that there are multiple posts about converting .cer to .pem, but none actually mention issues regarding the coversion. I have a cert named Cert.cer (original, I know) that I'm trying to convert to Cert_PEM.pem using the following command: openssl x509 -inform der -in Cert.cer -out Cert_PEM.pem In doing so I run into this error: 13892:error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag:tasn_dec.c:1316: 13892:error:0D07803A:asn1 encoding routines:ASN1_ITEM_EX_D2I:nested asn1 error:tasn_dec.c:380:Type=X509 I have some knowledge of certs, SSL and encryption, but this go (HowTos)