I am creating a telegram bot with the library "node-telegram-bot-api". I need to take users' images only in PNG format. As I understand it, Telegram converts images and creates JPEG, so I use both.downloadFile() to take PNG as a file and save it as PNG. However, it saves the users' image as JPEG. Code:

bot.on('document', message => {
   if(message.document.mime_type !== 'image/png') 
      return bot.sendMessage(msg.chat.id, `It is not png.`);

   let fileID = message.document.thumb.file_id;
   bot.downloadFile(fileID, path)
   .then(path => console.log(`Image saved: ${path}`))
   .catch(error => console.log(error));
});

result