打开并锁定一个文件（使用LockFile API函数）

var
  aHandle     : THandle;
  aFileSize   : Integer;
  aFileName   : String;

procedure TForm1.Button3Click(Sender: TObject);
begin
    aFileName    := 'C:\101\Java_new.pdf';
    aHandle      := CreateFile(PChar(aFileName),GENERIC_READ, , nil, OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,); // get the handle of the file

    aFileSize   := GetFileSize(aHandle,nil); //get the file size for use in the  lockfile function
    Win32Check(LockFile(aHandle,,,aFileSize,)); //lock the file
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
    Win32Check(UnlockFile(aHandle,,,aFileSize,));//unlock the file
    CloseHandle(aHandle);//Close the handle of the file.
end;

http://stackoverflow.com/questions/1916084/how-do-i-get-the-handle-for-locking-a-file-in-delphi