Open Microsoft Excel. Go to “ File > Options > Trust Center.” Now, click on the Trust Center Settings button. Select Protected View from the left side. Uncheck all the options on the right ...

You can make Excel always open old spreadsheets in Protected View. Enable or disable Protected View using in-built setting, Group Policy, Registry.

Microsoft Office 2010 includes a new "Protected View" that, by default, will open all Outlook attachments and documents downloaded from the Internet in "read-only" mode.