The Toggle Read Only feature can help Excel users easily switch active workbook between editing mode and read only mode. However, this feature does not show in Ribbon. This method will guide you to show the Toggle Read Only button in the Quick Access Toolbar easily.

1. Click the Arrow in the Quick Access Toolbar, and select the More Commands from the drop down list. See screenshot:

2. In the opening Excel Options dialog box, please do as follows:
(1) Select the Commands Not in the Ribbon from the Choose commands from drop down list;
(2) Click to highlight the Toggle Read Only in the commands list;
(3) Click the Add button.

3. Click the OK button to show this Toggle Read Only button on the Quick Access Toolbar, see screenshot:

4. Click the Toggle Read Only button  for the first time, active workbook switches to read only mode; click the Toggle Read Only button  once more, active workbook restores editing mode.

Notes:
(1) If you have never saved active workbook before, this Toggle Read Only button is invalid.
(2) When switching to read only mode, the following dialog box will come out if you have changed active workbook but not saved.

Lock current workbook to prevent it from being modified with only one click

Office Tab’s Lock utility can help Excel users one click to lock active workbook. If Excel users modified the locked workbook, warning message will come out to remind users when saving.