Ensure it is truly a video file and not Archivo de Descarga Katrin (2).mp4.exe .
Before opening any unknown .mp4 file, ensure it isn't a masked executable. Archivo de Descarga Katrin (2).mp4
If you are confident the file is safe, use a versatile media player to view it. Ensure it is truly a video file and
Search for "Katrin" or "Archivo" in your downloads history ( Ctrl+J or Cmd+Shift+J ) to see which website it came from. Archivo de Descarga Katrin (2).mp4