Word for Mac sometimes saves files without the extension (e.g., .doc, .docx or .rtf). If you're having trouble uploading a Word for Mac document, try these steps:
Open your document in Word.
Click File>Save As.
Choose a file format (.doc, .docx or .rtf).
Enter the name, and make sure that it ends with the correct extension (e.g., myfile.docx).
Try submitting this newly saved document.