G0ULI is correct. Don't worry, you're files haven't changed but the default app has been changed from Word 20xx to WordPad.
Two ways to fix this.
1. In File Explorer, right click on one of your .docx files and select Properties at the bottom of the context menu. In the General Tab, near the top, it should show Type of File and Opens With. The Opens With will probably say WordPad. If so, click on the Change button and select your version of Word from the list. Click OK and then click OK again to close Properties
2. To reset the default for all Word documents (.doc, .dot. etc.) to Word, click on the Start Menu (bottom left), then Settings, (the Cog symbol).
Double click on settings, then on Default apps in the left column.
Select "Choose default applictions by file type" near the bottom of the right column. In the new window, scroll down to the .doc* ahd .dot* file types (it can be a long list if you have a lot of programs). Each time you see WordPad as the default, left click on it and select Word instead.
Close the windows when finished.
Hope this fixes it.
Messy