First, let me assure you that moisture does not make fertilizers dangerous, nor does it reduce the viability or usefulness of the product, whatever brand or type you have purchased.
If water has not been introduced from outside the box, the reason it has gotten wet is probably because several of the nutrient compounds have water in them. For example magnesium sulfate, or Epsom Salt, has 7 parts of water, and some of the other compounds have lesser amounts. When these are mixed together, depending on the temperature and humidity where you are, it may cause them to melt together somewhat.
May I suggest you put your fertilizer in a plastic bucket, or even put the box inside a garbage bag. When you are ready to use it, just break it up, measure the amounts, and use it just as you would if it was dry.