If you are editing other people's documents the chances are enormous that they are not using the new features of Word, so you could simply saveas and return the document to the latest format before returning the document.
Perhaps easier still is to use a macro to insert the break e.g.
Code:
Sub InsertWord2010PageBreak()
'Graham Mayor - https://www.gmayor.com - Last updated - 17 Dec 2019
Dim oRng As Range
Set oRng = Selection.Range
oRng.Collapse 1
oRng.MoveStartWhile Chr(32), wdBackward
oRng.MoveEndWhile Chr(32)
oRng.Text = ""
oRng.InsertBreak wdPageBreak
oRng.MoveStart , -3
oRng.Select
If oRng.Characters.First = Chr(13) Then oRng.Characters.First.Delete
If oRng.Characters.Last = Chr(13) Then oRng.Characters.Last.Delete
lbl_Exit:
Set oRng = Nothing
Exit Sub
End Sub