This post gives the steps to enable copy/paste between Windows 7 and Ubuntu 16.04.3 on Oracle VM VirtualBox Version 5.2.12 r122591 (Qt5.6.2).
Install Guest Additions
1. In Ubuntu open a terminal and type sudo apt-get upgrade; (note 1: size of download)
2. Next, type sudo apt-get install build-essential module-assistant;
3. In the window running the VM, click Devices > Insert Guest Additions CD image...
4. In the “VBox_GSa_5.2.12” contains software intended to be automatically started. Would you like to run it? window click the Run button.
5. If prompted, enter your password and click the Authenticate button.
You will see:
Disregard the modeprobe vboxsf failed message. This failure will be cleared after you reboot.
6. Click the gear icon in the upper right corner and click Shut Down... then click the Restart button.
Enable and Test Copy/Paste
1. In the window around Ubuntu, click Devices > Shared Clipboard > Bidirectional
2. Open a Terminal and type nano
3. Type Testing 1,2,3 into the editor
4. Select Testing 1,2,3 with your mouse, right click Copy
5. Open Notepad in Windows
6. Right click in Notepad and select Paste
7. In Notepad type 4,5,6
8. Select 4,5,6 with your mouse, right click and select Copy
9. Back in nano, right click in the editor and select Paste
10. Type Control-X then type 'n' to exit nano
Enable and Test Shared Folders
1. In Windows create C:\winshare
2. In the window around Ubuntu, click Devices > Shared Folders > Shared Folders Settings...
3. Click the Folder with a + icon
4. For the Folder Path browse to C:\winshare
5. For the Folder Name: use share
6. Leave all checkbox unchecked and click OK and click OK again
7. Open a terminal in Ubuntu and type cd
8. Type mkdir share
9. Type sudo mount -t vboxsf share share (copy/paste works so you can copy paste this in)
Note on this step: you may need to use an absolute path for the second share, e.g. sudo mount -t vboxsf share /mnt/winshare
10. Type cd share
11. Type touch test.txt
12. Back in Windows look for C:\winshare\test.txt
13. In Windows create a file called test2.txt
14. Back in Ubuntu type ls, you should see test.txt and test2.txt
15. Type sudo umount ~/share to unmount the directory
Notes
1. sudo apt-get upgrade; downloads 365 MB on a fresh Ubuntu 16.04.3 image where "download updates during install" was not checked.
Reference
VirtualBox logo from [link]