There is a little-known feature in Word that displays readability statistics as part of the spelling and grammar check. Specifically, it tells you how many passive sentences there are and gives scores for Flesch Reading Ease and Flesch-Kincaid Grade Level.
I’ve written about readability metrics before. They’re not going to make you a great writer but they can stop you being a dreadful one. Find out how to switch on readability statistics in Microsoft word.