In word, Letter is the correct setting with the following size.
Height 27.94 and width 21.59.
If you wish to change to A4 then click on file on the word toolbar, choose page setup then the Paper tab. you will see where it says letter you can change to A4 from the drop down menu, then click on default tab.
In Publisher you set your margins each time you use it. To do this go to the toolbar and click on "arrange" then "layout" guides. j.