What makes it possible to store this uncooked fish product in the fridge for up to a month?
I feel I must offer a contradicting opinion to @rumtscho's answer.  The product you seem to have is indeed shown in the catalogue at the page of &quot;smoked salmon&quot; products, but note that it is the only one not being named &quot;cold smoked&quot;, but &quot;marinated&quot;.
And just by the looks of it I assume this is actually Gravlax: raw salmon, preserved by &quot;pickling&quot; in a marinade of lots of salt and sugar (and traditionally dill, but that's only for taste).  It will not taste like smoked salmon at all, because it isn't.   The marinade will be enough to prevent immediate bacterial growth (all the fluids go out by osmosis, and will turn into a highly saline brine), although in industry there are probably additional substances involved.
Gravlax is also easy to make on your own, in comparison to smoked salmon.  Just get a raw salmon filet of good quality, google the right proportions of sugar, salt, and dill, and massage them onto the meat.  Then you pack it in foil and leave it in the fridge for a couple of days.  (I wouldn't leave it for a month, though.)  You'll notice that the meat doesn't really cure, but gets stiffer, somewhat darker in color, and a bit &quot;glassy&quot;.