Preguntamos a la comercializadora por la distribuidora.

Because preguntar often takes an indirect object with a when you ask someone something or ask someone about something.

Here, la comercializadora is the person or entity being asked, so Spanish uses the personal a:

• Preguntamos a la comercializadora... = We ask / asked the supplier...

A very common pattern is:

• preguntar a alguien por algo = to ask someone about something

So in this sentence:

• a la comercializadora = the person/company you ask
• por la distribuidora = the thing/person/company you ask about

Because preguntar por means to ask about or sometimes to ask for / ask after, depending on context.

In this sentence:

• preguntar a alguien por algo/alguien = to ask someone about something/someone

So:

• Preguntamos a la comercializadora por la distribuidora
  = We ask / asked the supplier about the distributor.

Compare:

• Pregunté por María = I asked about María.
• Preguntamos por el técnico = We asked for/about the technician.

So por introduces the person or thing you want information about.

It can mean either one, because preguntamos is the same in both:

• present tense: we ask
• preterite: we asked

So without more context, the sentence is ambiguous.

Examples:

• Ahora preguntamos a la comercializadora por la distribuidora.
  = Now we ask the supplier about the distributor.
• Ayer preguntamos a la comercializadora por la distribuidora.
  = Yesterday we asked the supplier about the distributor.

Spanish often relies on context or time words to make this clear.

In Spain, these words are especially common in the electricity and gas sector.

• comercializadora = the company that sells you the service, handles your contract, bills you, etc.
• distribuidora = the company that manages the physical network/infrastructure in your area

So although a general translation might be supplier/retailer and distributor, the exact English term depends on the industry.

These words are feminine here because they refer to la empresa comercializadora and la empresa distribuidora, with empresa understood.

They are feminine because they are being used as feminine nouns, often with empresa implied:

• la comercializadora = la empresa comercializadora
• la distribuidora = la empresa distribuidora

In Spanish, adjectives and related nouns often agree with the implied noun. Since empresa is feminine, you get:

• comercializadora
• distribuidora

not the masculine forms comercializador / distribuidor.

Not with the same structure.

If you say:

• Preguntamos sobre la distribuidora

that sounds incomplete or unnatural in most contexts, because it does not clearly say who you asked. A more natural sentence would be:

• Preguntamos a la comercializadora por la distribuidora.

If you want to use sobre, it usually works better in different structures, for example:

• Hicimos una consulta sobre la distribuidora.
• Le hicimos preguntas sobre la distribuidora.

So with preguntar, por is the natural preposition in this pattern.

Normally, no. In this sentence, the articles la are needed because you are referring to specific entities:

• la comercializadora
• la distribuidora

Leaving them out would sound ungrammatical in standard Spanish.

Spanish uses definite articles more often than English does, especially with nouns referring to known people, companies, roles, or institutions.

The pattern is:

• preguntar + a + person/company + por + thing/person/company

So:

• Preguntamos = we ask / asked
• a la comercializadora = the company we ask
• por la distribuidora = what we ask about

You can build similar sentences the same way:

• Pregunté al vecino por el electricista.
• Preguntamos al banco por la transferencia.
• Le preguntaron a la tienda por el pedido.

This is a very useful structure to remember as a whole.

Yes, in real Spanish that is very common.

You will often hear:

• Le preguntamos a la comercializadora por la distribuidora.

That le repeats the indirect object (a la comercializadora). This is called clitic doubling, and it is very common in Spanish, especially when the indirect object is stated explicitly.

So both are possible:

• Preguntamos a la comercializadora por la distribuidora.
• Le preguntamos a la comercializadora por la distribuidora.

The version with le often sounds more natural in everyday Spanish.

Usually, but not always exactly.

Preguntar por can mean:

• to ask about someone/something
• to ask for someone, especially when trying to find them
• to ask after someone, in some contexts

Examples:

• Pregunté por Ana.
  = I asked about Ana. / I asked for Ana.
• Preguntó por ti.
  = He/She asked about you.
• Preguntamos por el encargado.
  = We asked for the manager.

In your sentence, the most natural meaning is ask about.