Putting up a wall where it already was

Hi I live in a co-op where a previous owner had taken down a wall to open up a small third bedroom into a dining area. We are actually interested in closing it back up for an office space. So we want to put a wall back up where it already was. In addition, just from having talked to the super who has been there forever and seen the way the other renovation work was handled (oy that kitchen) - I am pretty damn sure they never filed DOB permits to take the wall down in the first place. So I would bet anything that what is on file is that that room is still a bedroom. So would I need to file permits to put the wall back up? I mean I know the answer is probably yes but it really makes the project out of reach for us so I am reaching here...