If it's the official Microsoft Word viewer, you were just in time to download it. It's no longer available today! Be sure to backup the install program so you can use it iater, for example on a new PC your sister buys.
https://support.microsoft.com/en-us/help/891090/how-to-obtain-the-latest-word-viewer tells about alternatives. A good alternative they "forget" to mention is to install LibreOffice (a free open source replacement for the full MS Word) that can open .docx files.
If you prefer using the viewer: it only shows .doc files (up to Word 2003). If you want to show .docx files you need to install the Compatibility pack from https://support.microsoft.com/en-us/help/923505 . I hope it's still available. I didn't try.
Trying to help my sister. From time to time she gets a ‘document’ that she cannot open that was sent to her from a group that her husband is a member of. This time its a “docx” file. I saw that it is a ‘word’ document, found and downloaded the ‘word viewer’ but for whatever reason it would not work. “Kept” getting an error”. After looking around, I found a file converter at “ http://www.zamzar.com/” “ It worked just fine. But she would have to send me the file for me to convert and send back to her. Is there a replacement for the ‘word viewer’ that I can download and install on her computer that will resolve this issue.
Thanks in advance