How to add your own paper templates?
There have been several questions on how to have your own templates (Kanji practice paper, no texture, engineering paper etc).
There is an UNSUPPORTED way to add your own page template. Look in the
C:\Users\YOURLOGIN\AppData\Local\Packages\Microsoft.PlumbagoaMicrosoftGarageProject_8wekyb3d8bbwe\LocalState\PageTemplates and you will see the page templates. You can make a copy of a set of 4 and update them with your own paper template so it will now be in your list of templates. You will need to look at the image sizes for when it is portrait / landscape / grid view but you can do it.