Avant de rentrer, la secrétaire appelle le chauffeur afin qu’il s’arrête devant la papeterie.

Avant de + infinitive is used when the subject is the same as in the main clause, or when French leaves the subject unstated in a general way.

So here, avant de rentrer means before going back / before returning.

Compare:

• Avant de partir, je ferme la porte. = Before leaving, I close the door.
• Avant qu’il parte, je lui parle. = Before he leaves, I speak to him.

Use:

• avant de + infinitive → same subject or no explicit subject
• avant que + subjunctive → different subject

So in your sentence, avant de rentrer is the normal structure.

Rentrer usually means to go back, to return, or to go home/back inside, depending on context.

In this sentence, it most likely means something like:

• before going back
• before heading back
• possibly before going home

It does not necessarily mean a dramatic return in the English sense. In everyday French, rentrer is very common for simply going back somewhere.

Examples:

• Je rentre à la maison. = I’m going home.
• Il rentre au bureau. = He’s going back to the office.

Because afin de + infinitive is used when the subject is the same, while afin que + subjunctive is used when the subject is different.

Here:

• la secrétaire appelle = the secretary calls
• qu’il s’arrête = so that he stops

The secretary and the driver are different people, so French uses:

• afin que + subjunctive

Compare:

• Je ralentis afin de lire le panneau. = I slow down in order to read the sign.
  Same subject: I
• Je lui téléphone afin qu’il vienne. = I call him so that he comes.
  Different subjects: I / he

So afin qu’il s’arrête is correct because the person calling and the person stopping are not the same.

Because afin que normally triggers the subjunctive. It introduces a clause of purpose: so that / in order that.

So:

• afin qu’il s’arrête = so that he stops

The verb after afin que is in the subjunctive:

• que je m’arrête
• que tu t’arrêtes
• qu’il / elle s’arrête
• que nous nous arrêtions
• que vous vous arrêtiez
• qu’ils / elles s’arrêtent

This is not because the action is doubtful; it is simply the grammar required after afin que.

Because the intended meaning is to stop oneself / to come to a stop, which in French is usually s’arrêter.

• arrêter quelque chose / quelqu’un = to stop something / someone
• s’arrêter = to stop

Examples:

• Le chauffeur arrête la voiture. = The driver stops the car.
• Le chauffeur s’arrête. = The driver stops.

In your sentence, the driver is the one who stops, so French uses the reflexive verb:

• qu’il s’arrête

This is a spelling change found in some -eter verbs, including s’arrêter.

Infinitive:

• arrêter

Some present forms:

• j’arrête
• tu arrêtes
• il arrête
• qu’il arrête
• ils arrêtent

The è appears in forms where the syllable is pronounced openly. This is a normal spelling pattern, not a different word.

So:

• infinitive: arrêter
• subjunctive here: qu’il s’arrête

Afin que means so that or in order that.

It is very close in meaning to pour que, but afin que often sounds a bit more formal or polished.

So:

• afin qu’il s’arrête = so that he stops
• pour qu’il s’arrête = so that he stops

Both are correct in many contexts. In everyday speech, pour que is often more common. In careful written French, afin que is frequent.

Because appeler usually takes a direct object in French.

• appeler quelqu’un = to call someone

So:

• La secrétaire appelle le chauffeur. = The secretary calls the driver.

French does not say appeler à quelqu’un for this meaning.

Compare:

• J’appelle Marie. = I’m calling Marie.
• Ils appellent le médecin. = They’re calling the doctor.

Because que becomes qu’ before a word beginning with a vowel sound, such as il.

So:

• que il → qu’il

This is called elision. It is very common in French:

• que elle → qu’elle
• je aime → j’aime
• ne a → n’a

So afin qu’il s’arrête is simply the normal written form.

Devant means in front of.

So:

• s’arrêter devant la papeterie = to stop in front of the stationery shop/store

This is more precise than just saying à la papeterie, which could suggest being at the stationery shop in a broader sense.

Examples:

• Il attend devant la gare. = He is waiting in front of the station.
• La voiture s’arrête devant l’hôtel. = The car stops in front of the hotel.

No. This is a useful false friend.

In many everyday contexts, une papeterie means a stationery shop/store: a place where you buy paper, notebooks, pens, office supplies, and similar items.

Depending on context, papeterie can also refer more generally to paper goods, but in a sentence like this, devant la papeterie most naturally means in front of the stationery shop.

So don’t automatically translate it as paper mill or paper factory.

Because avant de rentrer is an introductory phrase placed at the beginning of the sentence.

French often uses a comma after this kind of opening element, especially in careful writing:

• Avant de partir, il ferme la fenêtre.
• Après le repas, nous sortirons.

The comma helps separate the time expression from the main clause:

• Avant de rentrer,
• la secrétaire appelle le chauffeur...

It is mainly a punctuation choice for clarity and rhythm.

Yes. A very natural alternative would be:

• Avant de rentrer, la secrétaire appelle le chauffeur pour qu’il s’arrête devant la papeterie.

That means essentially the same thing. The difference is mainly one of style:

• pour que = very common, neutral
• afin que = slightly more formal

So a learner should understand both.

Grammatically, the subject is not stated in the infinitive clause. In practice, it is usually understood from context.

In a sentence like this, it often refers to the main subject:

• la secrétaire

So the likely meaning is:

• Before going back / before returning, the secretary calls the driver...

However, because infinitives do not show person, the exact interpretation can depend on context. French allows that kind of compact phrasing when the meaning is already clear.

French usually uses definite articles much more often than English does.

So:

• la secrétaire = the secretary
• le chauffeur = the driver
• la papeterie = the stationery shop

In context, these are specific people/places already identifiable in the situation. French prefers the article here; leaving it out would be ungrammatical.

You generally cannot say:

• secrétaire appelle chauffeur

French needs the articles:

• La secrétaire appelle le chauffeur.