When you justify paragraphs, MS Word will equalize the spacing between words that are on the same line. If you think about, this is the only way your paragraphs can end up being aligned to both the left and right margins. Obviously, there are times when this can result in large unsightly spaces. The only way to avoid these unsightly spaces is to hyphenate some words. I don't use MS Office, but there should be a setting somewhere that will apply hyphenation for you automatically. You can check to see if this setting is on. Also, it's possible that "hyphenation" dictionaries may be available for you to install to help with this.