You are not allowed to edit this selection because it is protected.

We had some C# automation that worked fine with Word 2007/2010, but stopped with Word 2013 with the same "You are not allowed ..." warning.

Following steps on this site solved the issue.

Basically there are two settings to check:

• File – Options – General. Uncheck “Open E-Mail attachments and other uneditable files in reading view”
• File – Options – Trust Center – Trust Center Settings. Select Protected View, then clear all the checkboxes.