If you want to use SSL with your site in Azure you need to have a .pfx file.
We Apache you most likely have a certificate and a private key. I am using certificate from Letsencrypt.
Using openssl you can generate the .pfx file like this:
openssl pkcs12 -export -out /tmp/certificate.pfx -inkey /etc/letsencrypt/live/yourdomain.tld/privkey.pem -in /etc/letsencrypt/live/yourdomain.tld/cert.pem -certfile /etc/letsencrypt/live/yourdomain.tld/chain.pem
Replace yourdomain.tld with your actual domain name.
You will be asked for a password to protect the .pfx file