Is Impactful a Word?

Usually I don't pay a ton of attention when Microsoft Word doesn't know what I'm talking about. I use a lot of words it doesn't know and make up my own that mean weight loss pills that work. Even if they aren't words I think surely they should be. I stopped a little bit on the word "impactful" though. Certainly it’s a word right? The Merriam-Webster dictionary just took me to the word impact. Dictionary.com has "impactful" listed. Then there were a smattering of blogs insisting that it isn't. The Baltimore Sun says that you can use it with quotes around it.