Files with .VSSM extension are Microsoft Visio Stencil files that support provide support for macros. A VSSM file when opened allows running the macros to achieve the desired formatting and placement of shapes in a diagram. In general, Microsoft Visio is drawing software that allows creating files that can contain and represent user-defined information in different shapes.
You can also add watermark to many other file formats. Please see the complete list below.