uses

  ComObj;

// Replace Flags

type

  TWordReplaceFlags = set of (wrfReplaceAll, wrfMatchCase, wrfMatchWildcards);

function Word_StringReplace(ADocument: TFileName; SearchString, ReplaceString: string; Flags: TWordReplaceFlags): Boolean;

const

  wdFindContinue = 1;

  wdReplaceOne = 1;

  wdReplaceAll = 2;

  wdDoNotSaveChanges = 0;

var

  WordApp: OLEVariant;

begin

  Result := False;

  { Check if file exists }

  if not FileExists(ADocument) then

  begin

    ShowMessage('Specified Document not found.');

    Exit;

  end;

  { Create the OLE Object }

  try

    WordApp := CreateOLEObject('Word.Application');

  except

    on E: Exception do

    begin

      E.Message := 'Word is not available.';

      raise;

    end;

  end;

  try

    { Hide Word }

    WordApp.Visible := False;

    { Open the document }

    WordApp.Documents.Open(ADocument);

    { Initialize parameters}

    WordApp.Selection.Find.ClearFormatting;

    WordApp.Selection.Find.Text := SearchString;

    WordApp.Selection.Find.Replacement.Text := ReplaceString;

    WordApp.Selection.Find.Forward := True;

    WordApp.Selection.Find.Wrap := wdFindContinue;

    WordApp.Selection.Find.Format := False;

    WordApp.Selection.Find.MatchCase := wrfMatchCase in Flags;

    WordApp.Selection.Find.MatchWholeWord := False;

    WordApp.Selection.Find.MatchWildcards := wrfMatchWildcards in Flags;

    WordApp.Selection.Find.MatchSoundsLike := False;

    WordApp.Selection.Find.MatchAllWordForms := False;

    { Perform the search}

    if wrfReplaceAll in Flags then

      WordApp.Selection.Find.Execute(Replace := wdReplaceAll)

    else

      WordApp.Selection.Find.Execute(Replace := wdReplaceOne);

    { Save word }

    WordApp.ActiveDocument.SaveAs(ADocument);

    { Assume that successful }

    Result := True;

    { Close the document }

    WordApp.ActiveDocument.Close(wdDoNotSaveChanges);

  finally

    { Quit Word }

    WordApp.Quit;

    WordApp := Unassigned;

  end;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

  Word_StringReplace('C:\Test.doc','Old String','New String',[wrfReplaceAll]);

end;