If you need a PEM file without any password you can use this solution.
Just copy and paste the private key and the certificate to the same file and save as .pem.
The file will look like:
-----BEGIN PRIVATE KEY-----
............................
............................
-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
...........................
...........................
-----END CERTIFICATE-----
That's the only way I found to upload certificates to Cisco devices for HTTPS.