Media reports (including the one you link to) suggest that the mystery company is not just a foreign company, but a company owned by a foreign state. If correct, that rules out Deutsche Bank.
And, no, a document doesn’t have to be paper. Any record of evidence or information, anything which serves to document a fact or an event, can be a document.
But I don’t see anything saying Alfa Bank is state owned. Its a privately run Russian bank as far as I can work out (i know there is far less distinction between private and public run institutions in Putin’s Russian, but that doesn’t make a private company a state owned one AFAIK)