You probably use the Ctrl + Z Undo command to reverse the last action a lot in Word, but it also works just about anywhere in Windows. 

Rename a file in Word's File / Open dialog box or Windows Explorer and change your mind.  Immediately pressing Ctrl + Z will change the name back to the original. 

When you cut highlighted text in Notepad, Word, or most other places where you are editing text, Ctrl + Z will put the text back.  If you cut the text, then paste it somewhere else, hitting Ctrl + Z twice will undo both operations--putting the text back where it was cut from after first removing the pasted text. 

Drag a shortcut icon to your Desktop and change your mind. 

Ctrl + Z sends the icon back where it came from. 

Overfeathered an image in Photoshop?  Ctrl + Z undoes the damage.

If you send a deleted file to the Recycle Bin and change your mind, Ctrl + Z will bring it back.  NOTE:  If you hold down the Shift key to bypass the Recycle Bin while deleting a file, the file cannot be retrieved. 

If you ever make a mistake while moving files, renaming files or folders, pasting text, or performing a variety of other Windows tasks, Ctrl + Z is your best friend. 

And, if you make a mistake using Ctrl + Z, immediately press

Ctrl + Z again to undo the undo.