Click on a check-box to to add or remove a document type to or from the list of document types available when you right-click and select "New".
Drop a file into the window, and Tweak UI will automatically convert it into a document template.
If you have trouble creating a template, consult the Tweak UI template troubleshooter.
Highlight a document template and click the "Remove" button to remove that document template permanently instead of merely hiding it.
Some document templates cannot be removed.