Today I read Debian: convert ppk key for linux ssh which explained how to convert PuTTY *.ppk files to *.pem files for Linux:
sudo apt-get install putty-tools puttygen mykey.ppk -O private-openssh -o mykey.pem
Found a helpful article today, The Most Common OpenSSL Commands.
The particular command I needed wasn’t listed there though. What I needed to do was examine the contents of my Certificate Revocation List (CRL) certificate. I had a problem connecting to my website because it was complaining about an expired certificate and the culprit was indeed the CRL as I discovered when I ran:
$ openssl crl -inform CER -in ca.crl -text -noout