Using "Undo" command, you can undo actions, depending on the memory available to your system.
You can undo an action after you've saved a file, but not after you've closed and reopened it.

You can also undo any number of actions by reverting to the last saved version of the file.

To undo the last operation:

Choose Edit > Undo.

If an operation can't be undone, the command is dimmed and changes to Can't Undo.

Hotkey for this command is CTRL + Z.