When you add a mapped drive network location as a trusted location in Microsoft Office Word 2007 or in Word 2010, the location is added using the Universal Naming Convention (UNC) path.
For example, if you have a mapped drive of Z:\, the location is added as a trusted location using the following UNC path: \\server_name\folder_name.
This behavior is by design in Word 2007 and Word 2010. When you add the mapped drive as a trusted location, the drive mapping is translated or converted to the UNC path automatically. This behavior lets you see the actual location on the network that is trusted.
To add a mapped drive as a trusted location in Word 2007 or Word 2010, follow these steps:
In Word 2007 click the Microsoft Office Button, and then click Word Options.
In Word 2010 click File, and then click Options.
Click Trust Center.
Click Trust Center Settings.
Click Trusted Locations in the left pane.
Click to select the Allow trusted locations on my network (not recommended) check box.
Click Add New Location.
Click Browse, locate and select the mapped drive that you want to trust, and then click OK.
Click OK to close the Microsoft Office Trusted Location dialog box.