Hardboard & Paint

You didn’t say if you were planning to paint the laminate side or the back. If it is the laminate side you might get away with it if you first sand to give the paint sme tooth to hold onto and use a good quality primer like zinsars (sp). A sample test might be in order. The back side without the laminate should prime and paint fine.
If you are unsure I would probably return them and get some plywood. Good Luck

Hardboard has a few meanings, believe it or not, might be good to include a picture. Some will require special paints.

-- The mark of a good carpenter is not how few mistakes he makes, but rather how well he fixes them.

You won’t have any problem with painting hardboard, it will finish well, I would give it at least one coat on the back side (rough side) to seal it though.

If it is the “hardboard” I am thinking of…

-- Randy "You are judged as much by the questions you ask as the answers you give..."

ok, this is basically just melamine in quarterinch, rather than using chipboard for the core they use a masonite like core.

Basically, you sand the back side well and it will take paint. The plasitc side however may require a special laminate paint in order for the paint to actually stick.

-- The mark of a good carpenter is not how few mistakes he makes, but rather how well he fixes them.