There is only one file type that uses the .VTML extension:
Visual Tool Markup Language File
File created in the Visual Took Markup Language (VTML) format; allows developers to extend an application user interface with new language tags; often used for defining code hinting, code completion, and tag formatting functions.
VTML files are used by applications such as Adobe Dreamweaver. They are also used by older applications such as Adobe ColdFusion Studio, Macromedia HomeSite, and JRun Studio.
NOTE: VTML files more commonly use the .VTM extension.
Updated: March 16, 2019