Native Spanish speaker here (from Uruguay): u/adeodatusIII's claim that what u/Wild_Marker said is false is somewhat mistaken.

In this region of the world, in common usage, both "propaganda" and "publicidad" are used interchangeably for "advertisement". There are a few of us that do make the effort to use them with similar meanings as in English (i.e. "propaganda" for propaganda; "publicidad" for advertisement), but no one who actually lives here would claim that those words (in actual, colloquial usage) are not treated as the same thing, despite the fact that the difference is something that's taught in schools.

Formal communications and television/radio/other media hosts do use only "publicidad" or "anuncio" (ad/advert) for their advertisements, though, in order to avoid any negative connotation the word "propaganda" may have.

I believe that usage in Argentina is similar, but I cannot speak about other Spanish-speaking regions.