The title says all. I would like to have this option in right click menu on the desktop or in nautilus. I know that is possible, but I don't remember how to do this.
You may want to use
Templates directory (or how is called in your language) from your home directory in this sense. Files from this folder will appear in the
New Document menu. So, add the files with the extension what you want in this folder and you can create them after files with the same extension from the right click menu:
Moreover, if you add some predefined text in these files from
Templates folder, the new files which you will create them from the right click menu will contain that text.