I would go with @Randyr answer but I would change the read and convert method as follows for two reasons; 1) the output method requires storing all your answers when they wont be processed again and 2) good python apologises rather then asks for permission. 

    def read_and_convert_file(args):
        """Read the given input file and convert each hexadecimal value
        to decimal value and output to file
        """
        line_num = 0
        out_file = args['input_file'] + ".2decimal"
        with open(out_file, 'a+') as output:
            with open(args['input_file']) as input_file:
                for line in input_file:
                    line_num += 1
                    try: 
                        converted = str(int(line, 0))
                        output.write(converted + "\n")
                        print('Converted: {}'.format(converted))
                    except ValueError:
                        print('Invalid text on line',line_num)