Code:

unit FileMonitor;

interface

uses
  Classes, Windows, SysUtils;

type
  TFileMonitor = class(TThread)
  private
    FFileName: String;
    { Private declarations }
  protected
    procedure Execute; override;
    procedure DoSomething;
  public
    destructor Destroy; override;
    procedure StartMonitoring(Filename: String);
  end;

implementation

{ TFileMonitor }

destructor TFileMonitor.Destroy;
begin
  inherited;
end;

procedure TFileMonitor.DoSomething;
begin
  //tvoj kod za obradu promene
end;

procedure TFileMonitor.Execute;
var
  H: Cardinal;
begin
  H := FindFirstChangeNotification(PChar(FFileName), False, FILE_NOTIFY_CHANGE_LAST_WRITE or FILE_NOTIFY_CHANGE_FILE_NAME);
  if H = INVALID_HANDLE_VALUE then
    Terminate
  else
  try
    while not Terminated do
    begin
      WaitForSingleObject(H, INFINITE);
      if not FileExists(FFileName) then
      begin
        Terminate;
        break;
      end;

      Synchronize(DoSomething);

      if not FindNextChangeNotification(H) then
      begin
        Terminate;
        break;
      end;
    end;
  finally
    FindCloseChangeNotification(H);
  end;
end;

procedure TFileMonitor.StartMonitoring(FileName: String);
begin
  FFileName := FileName;
  Self.FreeOnTerminate := True;
  Resume;
end;

end.

Code:

TFileMonitor.Create.StartMonitoring('C:\Path\File.ext');