MS Word: keyboard shortcut for "Layout -> Breaks -> Page"
Alt followed by P followed by B followed by P.
This is the Ribbon shortcuts and will show up in tooltips after you press the Alt key. It is the equivalent of using the mouse.
Otherwise, you can create a macro and assign a keyboard shortcut to the macro. Here is my article on the Microsoft website on assigning keyboard shortcuts.
Here is such a macro:
Sub PageBreakInsert()
' Charles Kenyon
' Mimics insertion from Breaks menu
Selection.InsertBreak Type:=0
End Sub