I'd say D is the most correct, although in some cases it can sound demanding or abrupt. I don't write many business emails so I'm saying this from the perspective of someone who just speaks English. However it seems from this thread that others find "please find attached" to be satisfactory.
I also think these are fine to use: "Attached is a document...", "I have attached a document...", "Please see the attached document" / "Please see the document attached" (I do not agree with Yana that it cannot be used - there's nothing incorrect about it, though perhaps I'm missing some knowledge about business English here), or maybe even "I have included a document for your reference" if that is appropriate for what you want to say.