Pepperoni is a variety of Salami. Salami is a dried sausage which can be made of pork, beef, veal, horse, donkey, poultry or game. Different spices, smoking and vegetable ingredients give the different salame their particular taste.
Pepperoni limits its ingredients to beef pork and poultry and belongs to the more spicy varieties of salame.
I can't speak specifically to the shelf life of salami, especially considering all of the factors that come into play (source, type, age, storage, etc.), but when dealing with meat in general, you should never eat it if it smells or tastes "off". Smell is really the most reliable means of determining whether or not meat is still good - far more reliable than the use-by date.
It's unusual for meat to smell or taste sour as a result of foodborne bacteria; sourness is more likely to be due to rancidity of the fats, which is of course equally dangerous, albeit in a different way. Oxidation is very likely if the meat was not properly wrapped and/or stored in an airtight container.
Of course, many people have trouble telling the difference between spoilage due to rancidity and spoilage due to bacteria, and so what you're perceiving as rancid (sour) may really be bacterial spoilage.
Either way, if it tastes off, it's spoiled; don't eat it.
Best Answer
There's a difference between the title (is a sausiccon a type of salami), and the body (is there a difference).
The first is a question of classification, and no, a saucisson is type of cured sausage, but you'd want "saucisson sec" (dry sausage) for a dried, cured sausage with good storage characteristics like salami. So the relation is the other way around -- a salami is a type of saucisson.
"Differences" when you're dealing with general classifications such as this tend to be a question of if there are items that might fit into one category, but not the other. It's pretty obvious that salami is a narrower term than sausiccon, but I'm not sure if salami and sausiccon sec are just different names for the same concept, or if there might be items in one class that wouldn't fall into the other.
update : would sweet bologna be considered a saucisson sec ? It's only semi-dried, so I wouldn't classify it as a salami due to storage characteristics.