What the Undo and Redo toolbar buttons do may be obvious. You click the Undo button to reverse the effect of your last editing operation. And you click the Redo button to, in effect, undo the effect of your last Undo command. For example, if you've just copied data using the Copy and Paste buttons, you can click the Undo button to erase the effect of your copy-and-paste operation. If after clicking the Undo button, you realize that you've made a mistake because you did want the data copied, you can click the Redo button.
CAUTION: You can't undo the effect of all editing operations. In general, for example, you can undo the effect of Edit menu commands and their equivalent toolbar buttons but not the effect of File menu commands and their equivalent toolbar buttons. Occasionally, you may not be able to reverse an action because of memory limitations. For example, if you select an entire worksheet in Excel and then apply a formatting command, Excel may warn you that there is insufficient memory available to reverse the action.
It's useful to note that the Undo toolbar buttons available in Word, Excel, and PowerPoint will undo more than one editing operation. Similarly, the Redo toolbar buttons available in Word, Excel, and PowerPoint will redo more than one undo operation. To undo multiple editing operations, click the arrowhead next to the Undo toolbar button. Then, when the Office program displays a list of previous editing operations, click the oldest editing operation you want to undo. (The Office program undoes the selected editing operation, as well as every more recent editing operation.)
NOTE: The Outlook Standard toolbar doesn't provide an Undo or Redo toolbar button. Outlook's Edit menu does, however, provide Undo and Redo commands.
To redo multiple undo operations, click the arrowhead next to the Redo toolbar button. Then, when the Office program displays a list of undo operations, click the oldest undo operation you want to reverse. (The Office program reverses the selected undo operation as well as every more recent undo operation.)
NOTE: Access doesn't provide a Redo toolbar button—only an Undo toolbar button