{
 This function starts a hidden word instance, opens a specified document "ADocument"
 and replaces (all) occurrences of "SearchString" with a specified "ReplaceString".
 The function is similar to the Delphi StringReplace() function.
}
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;