I get it, you had good intentions to cook the salmon you recently purchased, but life happens and now it's been sitting in the refrigerator for a few days. Fresh salmon should be eaten 1-2 days for best taste. Sometimes up to three days if the salmon is well-packaged. Open up the salmon package and see how it smells. If it has a strong odor, feels slimy or you're just not sure, my advice would be throw it out.