code: public static boolean isPowerPacker(RandomAccessInputStream input) throws IOException
  	{
  		long pos = input.getFilePointer();
  		input.seek(0);
  		byte [] ppId = new byte [4];
  		input.read(ppId, 0, 4);
  		input.seek(pos);
  		return Helpers.retrieveAsString(ppId, 0, 4).equals("PP20");
  	}
docs: Will check for a power packer file
  @since 04.01.2011
  @param input
  @return true if this file is a powerpacker file
  @throws IOException