There have been some issues lately with MS updates to Office 365. nevertheless, that's a horribly inefficient way to go about the task! Try:
Code:
Sub Demo()
Application.ScreenUpdating = False
With ActiveDocument.Range
With .Find
.ClearFormatting
.Replacement.ClearFormatting
.Text = "[ ]{1,}^13"
.Replacement.Text = "^p"
.Forward = True
.Format = False
.Wrap = wdFindContinue
.MatchWildcards = True
.Execute Replace:=wdReplaceAll
End With
End With
Application.ScreenUpdating = True
End Sub