Microsoft does not provide Windows 7 any more. Try to find a pre-activated version instead.
Make sure to enable Guest Additions so that you can share folders.
Once the virtual machine is up, go to:
Then go to "my computer" and - double click on the CD icons. - also run the floppy disk.
Use "Auto-resize guest display".
Create a folder in your host that will be the shared folder. Like mkdir ~/Documents/vm_shared. Move the .exe there.
Now in Virtualbox, in the Windows window, go to:
Add that folder, make it auto-mount and permanent.
In a Windows guest, shared folders are browseable and therefore visible in
Windows Explorer. So, to attach the host's shared folder to your Windows
guest, open Windows Explorer and look for it under "My Networking Places" ->
"Entire Network" -> "VirtualBox Shared Folders". By right-clicking on a
shared folder and selecting "Map network drive" from the menu that pops up,
you can assign a drive letter to that shared folder.
But in windows 7, it will instead be at "My Computer". You may need to reset the VM.