Managing Word report layouts can be done in the Dynamics NAV application. You use the Report Layout Selection page, which you can find using the search box or in Administration, IT Administration, Reports:
When this window opens, it first loads a list of all the reports available in the application. You can filter the list on the top, as in the following example from Report ID 1306:
You can create or edit a custom layout for the selected report with the Custom Layouts and Run Report buttons.
When I select the Custom Layouts button, the Edit - Custom Report Layouts window opens:
As you can see, when you select the New… button, you can create a new Word and/or RDLC layout for the report. When you do this, a new line is added. You can then select the line and use the Import Layout, Export Layout, and Edit Layout buttons to manage the new layout.