Documents

When you open a protected document the Restrict Formatting and Editing task pane is automatically displayed
SS

This allows you to move between the editable regions of the document.
Find Next Region I can Edit -
Show All Regions I can Edit -
Highlight the regions I can edit -

If the task pane is closed and you don't have permission to edit a particular part of the document the following message will appear for a couple of seconds in the status bar.
SS
This modification is not allowed because the document is locked