If a document shows an odd behavior then you need to open it for repair. Before start repairing the document, open Windows Explorer and make a couple of copies of the file. These copies are insurance against the possibility that your efforts to open the document will end up trashing it further.
Start Word again, choose File > Open > Browse, select the document, click the drop-down arrow on the Open button, and choose "Open and Repair“.
If all goes well, Word will fix whatever is ailing the document and open it. It’s placed into a new document window, so the filename isn’t retained. This change is made so that you can save the repaired document under a new name, if you like, and keep the original.
Optionally, choose File > Save As and choose Rich Text Format in the “Save as type” drop-down list, and save the document as a rich text file. Close the document, and copy the rich-text document to a backup medium in case the problem returns.
Note: If Microsoft Word still can’t open the file and you have another word processor installed on your computer, try using it to open a damaged version of the document. Word processors such as WordPerfect and OpenOffice include text converters that can read most Word features but are fairly tolerant of document corruption, bypassing it as features they can’t interpret. Again, you’re likely to lose much of the document’s formatting, but you may be able to recover most of the text.