Todavía tengo pendiente llamar a la oficina y enviar el documento.

Here todavía means still: it shows that the speaker has not done these things yet.

In this sentence, todavía and aún are basically interchangeable:

• Todavía tengo pendiente llamar...
• Aún tengo pendiente llamar...

Both are natural. In everyday speech, todavía is often a little more common and a little less formal-sounding.

Tener pendiente is a very common expression meaning:

• to still have something left to do
• to have something pending
• to need to get around to something

So tengo pendiente llamar... is not literally about something physically hanging; it means the action is still unfinished.

You can use it with:

• a noun: Tengo pendiente una reunión.
• an infinitive: Tengo pendiente escribirle.

It is very natural in Spain.

It is singular because what follows is an infinitive phrase: llamar a la oficina y enviar el documento.

Spanish often treats an infinitive clause like a singular idea:

• Tengo pendiente llamar.
• Tengo pendiente terminar el informe.

But if you use a plural noun, then pendiente becomes plural:

• Tengo pendientes dos llamadas.
• Tengo pendientes varios documentos.

So the agreement depends on what is considered the thing that is pending.

Because after tener pendiente, Spanish commonly uses the infinitive to name the action that is still left to do.

So the structure is:

• tener pendiente + infinitive

Examples:

• Tengo pendiente hablar con Marta.
• Tenemos pendiente reservar el hotel.

In your sentence, the pending actions are:

• llamar a la oficina
• enviar el documento

Because llamar in the sense of to call / phone normally takes a before the person or place being called.

Examples:

• Llamé a mi madre.
• Voy a llamar al médico.
• Tienes que llamar a la oficina.

So a here is part of how the verb works in this meaning.

Because oficina is feminine: la oficina.

The contraction al only happens with a + el:

• a + el = al
• a + la = a la

So:

• Llamo al banco.
• Llamo a la oficina.

Because a belongs only to llamar:

• llamar a la oficina

The second verb, enviar, does not need that preposition in this sentence:

• enviar el documento

So the structure is:

• [llamar a la oficina] y [enviar el documento]

Each verb keeps its own pattern.

Spanish often uses the definite article where English might omit it.

Here el documento suggests a specific document that both speaker and listener can identify from context.

Compare:

• enviar el documento = send the document
• enviar un documento = send a document

In many real situations, Spanish prefers the article more often than English does.

Yes. That is also correct and very natural.

There is a small difference in feel:

• Tengo que... = I have to...
• Tengo pendiente... = I still have this on my to-do list / I still haven’t gotten around to it

So tener pendiente sounds a bit more like talking about unfinished business or tasks still waiting.

Yes, its position is natural.

• Todavía tengo pendiente llamar a la oficina... is very normal.

You may also hear:

• Tengo todavía pendiente llamar a la oficina...

But putting todavía near the beginning is especially common and clear.

It emphasizes that the task remains undone.

Yes, that is the most natural interpretation.

Because the object is la oficina, llamar a la oficina normally means to call the office by phone.

In other contexts, llamar can also mean:

• to call out
• to knock/call at a door
• to name

But in this sentence, phone is clearly the intended meaning.

Grammatically, it is one infinitive phrase made up of two coordinated actions:

• llamar a la oficina
• y enviar el documento

So after tengo pendiente, Spanish treats the whole sequence as one combined pending item.

But in meaning, of course, it refers to two things the speaker still needs to do.

Usually, no. In this structure, the normal form is:

• tener pendiente + infinitive
• tener algo pendiente

So you would say:

• Tengo pendiente llamar a la oficina.

Not usually:

• Tengo pendiente de llamar...

Spanish does use pendiente de in other contexts, for example:

• Estoy pendiente de tu respuesta.
• Está pendiente de los niños.

But that is a different construction.

Yes, it sounds very natural in Spain.

In Spain, tener pendiente is very common in everyday speech for talking about chores, admin, errands, and things on your to-do list.

For example:

• Tengo pendiente responder unos correos.
• Tenemos pendiente hacer la compra.
• Aún tengo pendiente pedir cita.

So the sentence sounds idiomatic and normal for Peninsular Spanish.