Is MDF hard or soft

The answer is relative. Most natural woods are tested for hardness on the Janka Scale to see if it is suitable for flooring. MDF is not typically used for that purpose and density of MDF can vary by manufacturer e.g. ultra-lite MDF. Based upon some anecdotal information it is not as hard as Maple but harder than Oak or Cherry.

To know for sure you will have to apply the Janka test to the sample you intend to use to quantify the hardness.