Marzipan and Almond Paste are both made out of almonds. This is the reason why some people assume that they are the same. They have some differences that should be noted. Marzipan is known to be smooth and sweet. There are some ingredients added to it so that it will be easier to shape. Some people even eat it on its own.
Almond paste is usually a lot less sweet. This is also coarser as compared to the marzipan. Almond paste is generally used for baking as a filler or to add a bit of taste to the goodies. Marzipan is already sweet enough, so some people eat this on its own.
The main difference between almond paste to marzipan is the number of almonds that these two have. The almond paste will have the same amount of almonds to sugar. It may also come with some other ingredients that can make this more flavorful, but the almonds to sugar ratio are the same.
With the marzipan, there will be a higher amount of sugar that is available. Some will even come with 75% more sugar as compared to the almond that the marzipan may have. Once again, other ingredients may be added to the marzipan to make it even more flavorful. You cannot interchange one for the other.