To view Word documents in .docx extensions, simply download free Word Viewer; you will also need to download the free Compatibility Pack as directed on the link.
Remember this is JUST for viewing - you will not be able to edit, save or create a Word document.
If you have a word processing need and don't want to spend $150 on Word, another option is Edit Plus. It's $35 and has spell check and word count - important features for authors.
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