Translation:Please open the door slowly.
I would have preferred the translation: Open the door gently, please. ゆっくり is often translated as slowly, but that's not really the full meaning. It means to take it nice and easy. When people get some time off, others will say "ごゆっくりなさい." or "ゆっくりしてしてください." Meaning take it easy/relax. It's a very nice thing to say to someone. It's not about going slow, per se, but taking a relaxed attitude.