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 "smoked salmon" products, but note that it is the only one not being named "cold smoked", but "marinated".

And just by the looks of it I assume this is actually Gravlax: raw salmon, preserved by "pickling" 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 "glassy".

Your salmon is not raw, it is smoked. This is a common conservation technique, and it is the reason why your fish has a long shelf life. The packaging has nothing to do with it.

You can confirm that this specific product is smoked by looking it up in the producer's catalogue, https://www.yumpu.com/en/document/read/63286903/vici-cataolog-en-2020-2021-web - you have to click through to page 23, Smoked salmon (vacuum packed).

The only packaging method that can prolong shelf life of meat and fish that I am aware of is packaging in oxygen-poor atmosphere. If done properly (which is not possible in a home kitchen), it can give you a few additional days of unopened shelf life, but not a whole month. It is unlikely to have been used for smoked fish.

It also depends on how the fish was killed. The two key helpers here that lead to a long shelf life even of non-preserved fish (i.e. not smoked, salted, pickled, marinated, dried, canned, etc.) are 1. exsanguination and 2. the utter destruction of the animal's CNS as quickly as possible. This can be achieved by sticking something pointy, like an awl, through its brain, then inserting a long thin stiff wire into its spine at a point just above the tail such that it runs through all the vertebrae and pops out of the other end, typically from the mouth, and finally making two ventral incisions (one just under the tail, one just under the gills) and letting out all the blood (and then eviscerating it, as normal). The fish is then very, very dead. A sign that this has been done properly is that almost no dark traces of blood remain attached to the untrimmed halves of the fish (though these will have been trimmed in the factory from pan-ready package fillets, removing the evidence). This technique is most used in Japan, where it is called ikejime (lots of videos online). Due to the time and skill involved, however, the result is an expensive product that almost never appears in supermarkets outside of Japan, but is sought after by top-end restaurants. Most fish sold around the world are simply left to suffocate, releasing all sorts of stress hormones that cause the flesh to spoil faster, though the difference only starts to kick in after a few days. No difference is perceptible between freshly-caught fish, however slowly they died. The industry globally will doubtless have invested in researching refinements to accelerate death that do not cost as much as paying an artisan to poke wires through backbones - an interesting avenue for further research - but that's all I can tell you today. I eat fish about one a year, and it's usually a grass carp that was swimming lethargically in a bucket only minutes earlier, which certainly eases the mind. @phipsgabler seems to have given you the most apt of your answers so far, so marinating is really the takeaway reason for the longevity (post-mortem) of your particular fish as depicted above.

Modern tech could allow this type of shelf life without smoking or brining using vacuum sealing and disinfection. Disinfection could be done by ozone, UV rays, chemicals like quats or ammoniums, ionizing radiation, etc. If all microbial activity is stopped, and no new microbes are allowed in, safety becomes almost a non-issue, and aesthetic concerns determine storage lifetimes.