When you want to call up that template, here's what you do. In your MS Word, click on 'File' (take note that you don't click on the File icon, but the word, 'File.' When you do so, a dialogue box appears from where you can choose the template you just created.
Click on 'Insert,' again at the top of MS Word. When the menu appears, let your mouse arrow hover over 'Picture.' Here you'll have several options. You can create your letterhead on the fly using some of those options. However, for our purposes we'll opt to choose 'From File,' since we already have a ready graphic. Click on the option, 'From File,' and a dialogue box opens. Locate your graphic and then click on it and then click the 'Insert' button. Your graphic will then appear inside the dotted box.