WHAT'S IN THE BOX?
I absent mindedly heard the Dutch, thought it was English (he opens the doors) and translated it to "hij opent de deuren" whoops, one of the perils of similar languages.
What is the difference between say this sentence and something like "Hij doet de deur open"?
Nothing, Hij opent de doos = Hij doet de doos open. Unlike English He does open the box. there is no difference in emphasis.
Why can't he open the "case"?
case would more likely be "koffer" or "kist(je)"