Store cocoa powder in a dark, cool, dry place, sealed against vermin. Dark and cool both slow the process by which volatiles (i.e., flavor) degrade. That said, don't keep it in the fridge or freezer unless sealed airtight, because both types of chill-chests are relatively humid environments. Humidity promotes mold, even on cocoa.
By the way, for future reference: When buying cocoa powder, note the manufacturer's suggested use-by date. Cocoa powder should last about three years, properly stored. If the use-by date is much less than that, look for another container.
The fleshy party of the fruit of theobroma cacao is is supposed to be sweet and pleasant. However, it does not taste like chocolate.
Chocolate is made from the nibs or seeds within the fruit of theobroma cacao, after it is fermented ground, and processed, and is in no way sweet.
The nibs themselves are very low in sugar, and contain alkaloids (such as caffeine or theobromine) which are bitter. This probably evolved to discourage predation or disease to the seeds themselves.
This is very similar to the way peach kernels (the seed within the pits) are not terribly sweet, although they certainly grow within a fruit that is.
So no—there is no such thing as naturally sweet chocolate.
A related tree, Cupuaçu (theobroma grandiflorum) is cultivated more specifically for its fruits, which are sweet and said to taste something like pineapple. Again, the fleshy fruit is not analogous to the seed which eventually becomes chocolate.
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I'm not familiar with that brand, but cocoa powder can be processed differently. The major categories are "natural" and "dutch processed", the latter being less acidic and having a somewhat milder flavor. And of course various brands may vary.