There is only one file type that uses the .OTG extension:
OpenDocument Graphic Template
Drawing template created using the OASIS OpenDocument standard; contains the default layout and drawing information for a vector graphic; stored in a file package using XML formatting.
OTG files can be used as a starting point for creating multiple .ODG drawings in OpenDocument-compatible programs, such as Apache OpenOffice (formerly OpenOffice.org).
Updated: January 21, 2014