In order to get the ArcGIS Diagrammer 10.3 to work in a Windows 10 environment, ArcMap 10.5, using Microsoft Visio Professional 2013
Make the following modifications in Microsoft Visio Trust Center:
Open Microsoft Visio, Click the "File" tab.
Click "Options"
Click "Trust Center"
Click "Trust Center Settings"
Click "File Block Settings"
Uncheck the "Open" option for the following:
"Visio 2003-2010 Binary Drawings, Templates and Stencils"
"Visio 200 - 2002 Binary Drawings, Templates and Stencils"
"Visio 5.0 or earlier Binary Drawings, Templates and Stencils"
Click "OK" until you can close.
ArcGIS Geodatabase Diagrammer for 10X
http://www.arcgis.com/home/item.html?id=a378b48be11b45b5bb25254643304cb7
Follow the publish directions that you download with the tool.
Now run the Geodatabase Diagrammer for 10X from ArcCatalog (Version 10.5) (again).
Best Regards,
Dixie Booker-Lair, GISP