The number and the municipal register are two different records kept by two different bodies. What the padrón is for, what the town hall usually asks to see, and what it quietly unlocks.
You have the keys, the boxes are in the hallway, and someone tells you that the next thing to do is "get on the padrón". It is good advice, and it is almost always given without any explanation of what the padrón actually is — which is how people arrive at the town hall with the wrong documents and leave with a new appointment instead of a certificate.
So, plainly: the padrón is the municipal register of the people who live in a given municipality. It is kept by the ayuntamiento, it records that you live at a specific address, and its central purpose is local. It is not the same as the NIE, which is a national identification number, and it is not the same as your residence status, which is a separate matter again. You can hold the number and not be on the register; you can be on the register and still have residence questions to resolve. Three records, three purposes.
What the town hall generally wants to see is your identification document and something proving your connection to the dwelling. For a straightforward rental that means the tenancy contract, and often a recent utility bill in the same name. Requirements are set locally and are revised from time to time, so check what Palma currently publishes before you go rather than working from a printout someone gave you last year.
The awkward cases are worth naming, because they are extremely common in the Balearic capital. Renting a room in a shared flat, living in a property owned by a relative, or holding a contract that has not yet been formalised all complicate the proof-of-address step. Municipalities have established ways of handling these, usually involving a signed authorisation from the person who holds the property. The mistake is assuming you cannot register at all and simply not trying.
What it unlocks is more than most newcomers expect. The local register is routinely referenced when you register with a health centre, when school places are allocated, and when you need to demonstrate to almost any administration that you actually live where you say you do. For residents of Mallorca and the wider islands, accredited residency is also part of how travel concessions for islanders are evidenced, and the certificate the town hall issues is typically what does the accrediting.
Keeping the record accurate is an ongoing obligation rather than a one-off errand. If you move within the same municipality, you update it; if you move to a different one, you register there. Some residents are also asked to confirm their entry periodically, depending on their circumstances. None of this is onerous, but an out-of-date register entry is exactly the kind of small inconsistency that causes a bigger process to stall months later.
The rule of thumb worth remembering in Palma: the number identifies you, the padrón locates you, and neither of them settles the question of your legal status here. Treat them as three separate jobs, do them in an order that suits your circumstances, and verify what the ayuntamiento is asking for today — through its own published guidance, or through a qualified adviser — whenever your situation is anything other than a standard tenancy.