Learn Spanish (Spain): Por favor, ¿puede usted firmar el documento?

usted is the formal "you" in Spanish. You use it to show respect, like when talking to someone older, a client, or a person you don't know well. Asking someone to sign a document is usually a professional or official situation, so usted is the polite choice.

If usted means "you", why does the verb puede look like the "he/she" form?

That is the special rule for usted! Even though it translates to "you", grammatically it always uses the exact same verb endings as él (he) and ella (she). If we were using the informal tú, the verb would be puedes.

Why does usted come right after puede instead of at the beginning of the sentence?

In Spanish questions, it is very common to invert the word order, placing the subject (the person doing the action) immediately after the verb. You could technically say ¿Usted puede firmar...?, but ¿Puede usted firmar...? sounds much more natural for a question.

Why is the word for "sign" left as firmar instead of being conjugated?

When you put two verbs together to express a single idea (like "can sign"), only the first verb changes to match the person doing the action. Since the first verb is already conjugated as puede, the second verb stays in its raw, dictionary form (the infinitive), which is firmar.