I have now created a new VM on VirtualBox, configured the machine settings by clicking "Machine -> Settings -> General -> Advanced" and then set:
"Shared Clipboard" and "Drag'n Drop" as "Bidirectional",
then installed and mounted the Guest Additions.
But if I try to copy and paste something to VirtualBox VM, it doesn't work at all and if I click on "Devices->Insert Guest Addditions CD Image" I get the error: "Unable to insert the virtual optical disk ...".
Do you maybe know how I can fix this?
Host OS: Windows 8.1
Guest OS: Ubuntu 18.04.1
Thanks a lot in advance