I need that Ubuntu has internet and also can connect to the VPN using VirtualBox adapters installed in Windows. – Ale (from comments above)
Welcome to the networking hell of VPNs and Virtual Machines. You have two things you want to achieve: You want Ubuntu to be able to go out to the internet, but to also be able to use the VPN. You have a big problem: You cannot achieve both at the same time. The nature of VPN networking is that all data gets routed through the VPN. With the VPN existing on the Windows host, that means anything going over the Windows connection via the Virtual NAT adapter will be subject to that routing as well.
You'll have to investigate the policies of the network that your Windows system is on (EXCLUDING the VPN part) to follow this recommendation, and check the compatibility of your network equipment with 'Bridged' mode in VBox, but the sorta-simplest option is to add a second virtual network adapter and hook it up to "Bridged adapter" and have that set to the network card you want to be 'acted' as (or in laymans terms, the network card which is what your host system communicates with the LAN over, so either wireless or ethernet depending on the networking method). That way, you have a non-VPN'd 'connection' via whatever the standard network is that your computer is connected to, separate from the NAT'd (VPN'd) connection.
The tricky part is this: You have to know VirtualBox enough to be able to manually disable one network connection and enable the other on the VM's hardware controls to switch between them. One would be NAT out over the Windows computer and would go over the VPN when the Windows computer is connected to the VPN. The other would be Bridged Network out onto the network that your Windows computer is connected to directly without going over the VPN. However, you have to do a lot more manual work to achieve this.