Your sample file shows that each payslip has two lines that begin with the employee number and that some have leading spaces. The following macro seems to do the job on that file.
Code:
Sub Cleanup Payslips()
With Selection.Find
.ClearFormatting
.Replacement.ClearFormatting
.Text = "^p^p^p^p"
.Replacement.Text = "^p^p"
.Forward = True
.Wrap = wdFindContinue
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Execute Replace:=wdReplaceAll 'tighten large spaces a bit
.Text = "^13 [0-9]{7} "
.Replacement.Text = "^m^&"
.MatchWildcards = True
.Execute Replace:=wdReplaceAll 'add page breaks if leading spaced
.Text = "^13[0-9]{7} "
.Replacement.Text = "^m^&"
.MatchWildcards = True
.Execute Replace:=wdReplaceAll 'add page breaks if not leading spaced
End With
End Sub