"cat" will output the file sequentially, so it would work best with plain text. ".docx" is a Word document.
(See the man page for "cat": )
Code:
man cat
Or...
Are you asking why the file isn't recognized because of spaces in the filename? ("cat" still won't work, but the following would help when using a filename with special characters in general)
You can either enter it contained in quotes:
Code:
man "sunny windy day.docx"
Or, by using the '\' character to denote a special character: