How can I convert a PFX certificate file for use with Apache on a linux server?

With OpenSSL you can convert pfx to Apache compatible format with next commands:

openssl pkcs12 -in domain.pfx -clcerts -nokeys -out domain.cer
openssl pkcs12 -in domain.pfx -nocerts -nodes  -out domain.key   

First command extracts public key to domain.cer.
Second command extracts private key to domain.key.

Update your Apache configuration file with:

<VirtualHost 192.168.0.1:443>
 ...
 SSLEngine on
 SSLCertificateFile /path/to/domain.cer
 SSLCertificateKeyFile /path/to/domain.key
 ...
</VirtualHost>

Additionally to

openssl pkcs12 -in domain.pfx -clcerts -nokeys -out domain.cer
openssl pkcs12 -in domain.pfx -nocerts -nodes  -out domain.key

I also generated Certificate Authority (CA) certificate:

openssl pkcs12 -in domain.pfx -out domain-ca.crt -nodes -nokeys -cacerts

And included it in Apache config file:

<VirtualHost 192.168.0.1:443>
 ...
 SSLEngine on
 SSLCertificateFile /path/to/domain.cer
 SSLCertificateKeyFile /path/to/domain.key
 SSLCACertificateFile /path/to/domain-ca.crt
 ...
</VirtualHost>

To get it to work with Apache, we needed one extra step.

openssl pkcs12 -in domain.pfx -clcerts -nokeys -out domain.cer
openssl pkcs12 -in domain.pfx -nocerts -nodes  -out domain_encrypted.key
openssl rsa -in domain_encrypted.key -out domain.key

The final command decrypts the key for use with Apache. The domain.key file should look like this:

-----BEGIN RSA PRIVATE KEY-----
MjQxODIwNTFaMIG0MRQwEgYDVQQKEwtFbnRydXN0Lm5ldDFAMD4GA1UECxQ3d3d3
LmVudHJ1c3QubmV0L0NQU18yMDQ4IGluY29ycC4gYnkgcmVmLiAobGltaXRzIGxp
YWIuKTElMCMGA1UECxMcKGMpIDE5OTkgRW50cnVzdC5uZXQgTGltaXRlZDEzMDEG
A1UEAxMqRW50cnVzdC5uZXQgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkgKDIwNDgp
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEArU1LqRKGsuqjIAcVFmQq
-----END RSA PRIVATE KEY-----

Took some tooling around but this is what I ended up with.

Generated and installed a certificate on IIS7. Exported as PFX from IIS

Convert to pkcs12

openssl pkcs12 -in certificate.pfx -out certificate.cer -nodes

NOTE: While converting PFX to PEM format, openssl will put all the Certificates and Private Key into a single file. You will need to open the file in Text editor and copy each Certificate & Private key(including the BEGIN/END statements) to its own individual text file and save them as certificate.cer, CAcert.cer, privateKey.key respectively.

-----BEGIN PRIVATE KEY-----
Saved as certificate.key
-----END PRIVATE KEY-----

-----BEGIN CERTIFICATE-----
Saved as certificate.crt
-----END CERTIFICATE-----

Added to apache vhost w/ Webmin.