We have found one software suitable in our database for this conversion.
The only way to convert vssx to vss, aka Visio stencils to shapes, would be to open the .vssx files in Microsoft Visio 2013, right click on the stencil header, select Save As, and pick the .vss as the desired file type. This will save it to a VSS format (smart shapes data).
Updated: January 10, 2017
A diagram application, that uses vector graphics to create diagrams. Microsoft Visio is distributed as part of Microsoft Office Family and also available as a subscription through Microsoft Office 365. The latest version is Visio 2016 that is compatible with Windows 7, Windows 8 and Windows 10.