Sub UpdateDocuments()
Application.ScreenUpdating = False
Dim strFolder As String, strFile As String, strDocNm As String, wdDoc As Document
strDocNm = ActiveDocument.FullName
strFolder = GetFolder
If strFolder = "" Then Exit Sub
strFile = Dir(strFolder & "\*.doc", vbNormal)
While strFile <> ""
  If strFolder & "\" & strFile <> strDocNm Then
    Set wdDoc = Documents.Open(FileName:=strFolder & "\" & strFile, AddToRecentFiles:=False, Visible:=False)
    With wdDoc
      Call FindRep(wdDoc, "String to Find", "String for Replacement")
      .Close SaveChanges:=True
    End With
  End If
  strFile = Dir()
Wend
Set wdDoc = Nothing
Application.ScreenUpdating = True
End Sub

Function GetFolder() As String
Dim oFolder As Object
GetFolder = ""
Set oFolder = CreateObject("Shell.Application").BrowseForFolder(0, "Choose a folder", 0)
If (Not oFolder Is Nothing) Then GetFolder = oFolder.Items.Item.Path
Set oFolder = Nothing
End Function

Sub FindRep(wdDoc As Document, StrFind As String, StrRep As String)
With wdDoc.Range
  With .Find
    .ClearFormatting
    .Replacement.ClearFormatting
    .Text = StrFind
    .Replacement.Text = StrRep
    .Forward = True
    .Wrap = wdFindContinue
    .Format = False
    .MatchCase = False
    .MatchWholeWord = False
    .MatchWildcards = False
    .MatchSoundsLike = False
    .MatchAllWordForms = False
    .Execute Replace:=wdReplaceAll
  End With
End With