Tengo que adjuntar un justificante para la baja médica.

Both can express obligation, but tener que + infinitive is extremely common in everyday Spanish.

• Tengo que adjuntar... = I have to attach...
• Debo adjuntar... = I must / I should attach...

In many contexts, tener que sounds more neutral and conversational. Deber can sometimes sound a bit more formal, stronger, or more like duty, depending on context.

So in ordinary workplace or administrative Spanish, tengo que is a very natural choice.

Spanish often drops subject pronouns because the verb ending already shows who the subject is.

• Tengo clearly means I have
• So yo is unnecessary unless you want emphasis or contrast

For example:

• Tengo que adjuntar un justificante. = normal
• Yo tengo que adjuntar un justificante, no tú. = emphasized contrast

Omitting yo is one of the most normal features of Spanish.

Adjuntar means to attach, especially in administrative, digital, or formal contexts.

Common examples:

• Adjuntar un archivo = to attach a file
• Adjuntar un documento = to attach a document
• Adjuntar un justificante = to attach a supporting document / proof

In Spain, adjuntar is very common in emails, forms, HR communication, and official procedures.

You may also hear anexar, but adjuntar is generally the more everyday and standard option in this kind of sentence.

A justificante is a document that serves as proof, evidence, or supporting documentation.

Depending on context, it might be:

• a doctor’s note
• a receipt
• proof of payment
• proof that something is justified or officially documented

In this sentence, it most likely means some kind of medical proof document, such as a certificate or note needed to support the sick leave.

So justificante is not just a general explanation; it usually refers to an actual document.

These words are related but not the same.

• un justificante = a supporting document / proof
• una justificación = a justification / explanation

If you need to upload or attach paperwork, justificante is the natural word.
Justificación would focus more on the reason or explanation itself, not necessarily the document.

So in office or HR language, adjuntar un justificante is the standard wording.

In Spain, baja médica is the normal term for medical leave or sick leave.

Literally:

• baja can mean a leave, removal, or being signed off
• médica means medical

So la baja médica refers to the official period when someone is not working for health reasons, usually with medical authorization.

This is very common Spanish-from-Spain workplace vocabulary.

Spanish often uses the definite article where English might not.

Here, la baja médica refers to the specific concept or process of being on sick leave. In Spanish, that sounds natural with the article.

Compare:

• para la baja médica = for the sick leave / for medical leave
• not using the article here would sound less natural

This is very common in Spanish with abstract or institutional things:

• ir al médico
• tener la gripe
• pedir la baja

Because médica agrees with baja, which is a feminine noun.

• la baja → feminine singular
• so the adjective must also be feminine singular: médica

This is standard adjective agreement in Spanish.

Examples:

• el informe médico
• la baja médica
• los certificados médicos
• las pruebas médicas

Here para means for in the sense of intended for or needed for a purpose.

• un justificante para la baja médica = a document needed for / used for medical leave

If you said de la baja médica, it would sound more like of the medical leave or about the medical leave, which is a different relationship.

So para works well because the document is being attached for the purpose of processing or supporting the sick leave.

Yes. Adjuntar is normally used directly with its object.

• Adjuntar un justificante
• Adjuntar un archivo
• Adjuntar una copia del DNI

So the structure is:

adjuntar + noun

English speakers sometimes expect an extra word because English often uses attach + noun, but Spanish works directly too, with no extra preposition needed before the object.

Yes, but it changes the nuance slightly.

• Tengo que adjuntar... = I have to attach...
• Necesito adjuntar... = I need to attach...

Both are correct, but tengo que emphasizes obligation, while necesito emphasizes necessity.

In administrative contexts, tengo que often sounds more like this is a requirement, which fits this sentence very well.

It is fairly neutral and suitable for everyday professional or administrative use.

It is not especially casual, but it is also not overly formal. It would sound natural in contexts like:

• speaking to HR
• filling out a form
• writing an email
• explaining a requirement

If you wanted to sound more formal in writing, you might use something like:

• Debo adjuntar un justificante para la baja médica.
• Es necesario adjuntar un justificante para la baja médica.

But the original sentence is perfectly standard and natural.