I wouldn't use mud to fill the improfections of the wood. It is likely to flake off. I would use spackle instead and use a drywall sanding pad to sand it with. Try not to sand it completely down because the improfections will come back on you but sand it flat and finish the job of leveling with primer. I think it's likely the shiny substance you are calling lacquer is the adhesive they put the board together with.