OpenSSL generate .PFX file

openssl pkcs12 -inkey STAR.example.com_key.txt -in STAR.example.com.crt -export -out example_pfx.pfx

OPENSSL PFX 

On Windows server to properly import you may need to specify encryption

openssl pkcs12 -macalg SHA1 -keypbe PBE-SHA1-3DES -certpbe PBE-SHA1-3DES -export -out website.pfx -inkey private.key -in a01f36fe692456.crt -certfile gd_bundle-g2-g1.crt