Ubuntu distribution uses nautilus as the default file manager. You can tweak nautilus to increase your productivity. Here is one hack which I discovered recently. When you right click on the desktop or inside your file manager you get a menu as shown in the screen shot below.
Copy invoice.odt to ~/Templates directory . ( Templates directory will be automatically created under your home folder in Ubuntu)
$ cp invoice.odt ~/Templates
Now see the right click menu. It will look like the screen below.
You can add as many templates as you like . Also, it is possible to group together templates by creating folders under ~/Templates directory. See the figure below. I have some groupings inside my template directory.