Sub MonTest()
    Dim objDoc As Document, Phrase As Range
	Set objDoc = Application.Documents.Open("D:\Documents\word\nom du document.docm")
    'selection du document
    Selection.WholeStory
    'effacer l'ancienne couleur
    Selection.Range.HighlightColorIndex = wdNoHighlight
    ' selectionner phrase par phrase
    For Each Phrase In objDoc.Sentences
        Phrase.Select
        couleur
    Next
    Selection.EndKey Unit:=wdStory
End Sub
Sub couleur()
    Dim machaine As String
    With ActiveDocument.Bookmarks
        .Add Range:=Selection.Range, Name:="Suite"
    End With
    Selection.GoTo What:=wdGoToBookmark, Name:="Suite"
    machaine = Selection
    x = Len(machaine)
    If x > 50 Then
        Selection.Range.HighlightColorIndex = wdPink
    End If
End Sub