The text with errors causes irritation and distrust of the author. The article should be free of errors, at least from the point of view of Word. But Word, underlining words or sentences with errors, will not show you, for example, extra spaces in the text.
And this is definitely a mistake. I don't recommend relying heavily on literacy testing services. They still won't fix the mistakes for you. Better improve your own literacy. With each article, believe me, there will be fewer and fewer mistakes.