If you want to make changes to the default settings that load up every time you open a Word document (the font, size, layout settings, etc), you can achieve it by editing the normal.dotm file, a template file that Microsoft Word uses to store those default settings. Any changes you make to this file therefore apply to every new document you make.

To edit this template, navigate to C:\Users\username\AppData\Roaming\Microsoft\Templates and open the normal.dotm file. You will be able to edit this template like any other Word document, but any changes you save to the file will apply to new documents you open in the future. It is advisable to copy the file before you start editing it, to back up any settings you may have already saved. If you ever need to restore the original default settings, simply delete normal.dotm and Word will rebuild the original template.