The new document templates available from the File->New from Template menu or the New button on the File Toolbar can be edited or added to by editing the existing template text files or adding new text files.
There are current-user templates and all-user templates. The current-user templates are specific to the current-user only and are stored in a separate folder than the all-user templates. By default, only all-user templates are installed, but current-user templates may be added by a user.
Note that when the template menu is created, current-user templates appear before all-user templates and the template filenames are alphabetized.
Ending the template filename with a '-' causes it to be a separator. Example: "MyNewTemplate-.txt". The actual filenames ending in '-' will not appear in the template menu because they will only result in a new separator. The filename before the '-' is used to determine where the separator will go because it is alphabetized with the other filenames.
For more information and the locations of the template folders, select File->New from Template->Quick Help.