It is OpenVPN 2.4 manual, now version 2.5 is actual: https://openvpn.net/community-resources/reference-manual-for-openvpn-2-4/
It is OpenVPN 2.4 manual, now version 2.5 is actual: https://openvpn.net/community-resources/reference-manual-for-openvpn-2-4/