You’ll have seen preview images when you open a file in Word. If you choose File > Open and, from the Views option list you choose Preview, you will see either a small image of the full page or some of the text on the page. All this begs the question of what determines what you see?
The full page preview is an option when you save a file in Word. To configure it, choose File > Properties > Summary tab and enable the Save Preview Picture checkbox. Now, when you save the file it will have a preview image saved with it which will show in the preview area.
To ensure the Properties dialog appears everytime you save a file the first time so you can configure the Save Preview Picture option, choose Tools > Options > Save tab and enable the checkbox for Prompt for Document Properties.