Learn Portuguese (Portugal): O produto chegou estragado, pelo que anexo o recibo para a troca. - The product arrived damaged, therefore I attach the receipt for the exchange.

Pelo que is a formal connector meaning "therefore," "so," or "which is why." It introduces the logical consequence of the previous clause (the product arriving damaged). It is very common in professional emails, customer service interactions, or formal written Portuguese.

Does pelo que trigger the subjunctive mood here?

No. Pelo que is a conclusive connector that introduces a definite fact or a direct result. Because you are stating the reality of your current action (attaching the receipt), it takes the present indicative form anexo.

Is the word anexo in this sentence a noun or a verb?

Here, anexo is the first-person singular present tense of the verb anexar (I attach). While you might often see it as a noun (o anexo, meaning the attachment) or in the phrase em anexo (attached), in this specific structure it functions as an active verb.

Why do we use para instead of por before a troca?

We use para because it expresses the specific purpose or final goal of the action (in order to process the exchange). If you were talking about the actual substitution of one item for another, you would use por (for example, trocar o produto estragado por um novo).