Hello, I am an independent consultant willing to help.
Create a new page template:
1 In the list of pages on the right side of the screen, choose Add page.
2 Choose View> Paper Size.
3 In the Paper Size task pane, set the paper size and printing margins.
4 Add the content you want to appear in the template.
5 All the new pages that are created with this template will have this information in it.
6 When finished, choose Save Current Page as a template at the bottom of the Paper Size task pane.
7 In the Save As Template dialog box, name the template and click Save.
Source: https://support.office.com/en-us/article/crear-...
I hope this information will be useful.
Best regards,
Cristhian