MS Office makes it easy to assign custom keyboard shortcuts to any Word menu item using the Customize dialog box. Here are the steps to take.

If you have several pre-defined blocks of content in Microsoft Word, you can avoid the busy Quick Parts gallery by assigning keyboard shortcuts.

How to Create a Shortcut for a Start Menu Item in Windows 7 Pro. Although some people like to keep a sparse, clutter-free desktop, others may prefer to fill it with shortcuts.

Then right-click on the shortcut, go to Properties, and add a space and /mfile1 after the path in the Target field. You should rename the shortcut to reflect it'll open your last used document.