Learn Portuguese (Portugal): Todos quantos compram este produto sabem que é pré-embalado. - Everyone who buys this product knows that it is prepackaged.

In Portuguese, the prefix pré- always takes a hyphen when it has its own stress, which is indicated by the acute accent. This is a strict rule for the stressed prefixes of time and hierarchy pré-, pós-, and pró-. Because of this, it is never merged directly into the base word as it often is in English.

Does the prefix pré- change the gender or number of embalado?

No, prefixes like pré- do not affect inflection. The base word embalado is an adjective here, so it still must agree with the masculine singular noun it refers to, which is este produto. If the product were a feminine noun like esta caixa, it would become pré-embalada.

I usually say todos os que for 'everyone who'. What is todos quantos?

Todos quantos is an excellent alternative to todos os que or toda a gente que. It translates to 'all those who' or 'as many as'. At the B2 level, using quantos as a relative pronoun after todos makes your Portuguese sound very natural and slightly more elevated.

Why is compram in the present indicative and not the subjunctive?