Download & install iso file

sudo apt-get install virtualbox-guest-additions-iso

If during the installation process there is an error as below

could not get lock /var/lib/dpkg/lock-frontend

Then execute the following series of commands

sudo killall apt apt-get

sudo rm /var/lib/apt/lists/lock
sudo rm /var/cache/apt/archives/lock
sudo rm /var/lib/dpkg/lock*

sudo dpkg --configure -a

sudo apt update

Mount file iso

After downloading the iso file, mount it with ubuntu

Enter your password if you have one, and select "Run"

Change copy setting

Device > Share Clipboard > Bidirectional

Restart the computer and enjoy the results.