Visio Stencil File(.vss) are stencil files created with Microsoft Visio 2007 and earlier. Stencil files provide drawing objects that can be included in a .VSD Visio drawing.
Learn more about this file format here
GroupDocs.Viewer (in GroupDocs.Viewer.dll) Version: 20.9
public static readonly FileType VSS
Public Shared ReadOnly VSS As FileType
static initonly FileType^ VSS