Avant d'envoyer le dossier, il faut sauvegarder le document.

Because French usually shortens de to d' before a vowel sound. This is called elision.

So:

• de + envoyer → d'envoyer

The same thing happens in many common expressions:

• d'aller
• d'être
• douvrir would actually be d'ouvrir

In your sentence, avant de becomes avant d' because envoyer starts with a vowel sound.

Because after avant de, French normally uses the infinitive when the subject is understood to be the same or when the action is expressed in a general way.

So:

• avant d'envoyer le dossier = before sending the file

This is a very common pattern:

• avant de partir = before leaving
• avant de manger = before eating
• avant de commencer = before starting

If French uses a different subject after before, it often switches to avant que + subjunctive instead.

For example:

• Avant qu'il parte... = Before he leaves...

Il faut is an impersonal expression meaning something like:

• it is necessary
• one must
• you have to
• it’s necessary to

So in this sentence:

• il faut sauvegarder le document

means:

• you have to save the document
• the document must be saved
• it is necessary to save the document

The il here does not refer to a person. It is just part of the fixed expression il faut.

Because il faut is more general and less directly aimed at one specific person.

Compare:

• Il faut sauvegarder le document.
  = It is necessary to save the document. / You have to save the document.
  This sounds general, like an instruction.

• Tu dois sauvegarder le document.
  = You must save the document.
  This speaks directly to you.

In instructions, manuals, rules, and procedures, il faut is very common because it sounds neutral and impersonal.

They are related, but they are not exactly the same.

• dossier often means a file, folder, or application packet
• document means a document

So the sentence suggests something like:

• before sending the file/folder/application
• you must save the document

This can make sense in a computer context or an administrative context. For example, you may be sending a file or case folder, but the specific thing you need to save is the document itself.

A learner might expect the same word in both places, but French is distinguishing between two different objects.

French usually requires an article where English often does not.

So French says:

• le dossier
• le document

Even if English might say:

• before sending the file
• save the document

or sometimes just:

• before sending a file
• save document

French normally wants the article. Here, le refers to a specific file and a specific document already known from the context.

That opening phrase sets the time relationship first:

• Avant d'envoyer le dossier = Before sending the file

Then the main clause gives the required action:

• il faut sauvegarder le document = you must save the document

This is very natural in French. It is similar to English instructions like:

• Before submitting the form, you must sign it.

French often places this kind of before/after phrase at the front when giving instructions.

The comma is very natural here because the sentence begins with a longer introductory phrase:

• Avant d'envoyer le dossier, il faut sauvegarder le document.

It helps separate the introductory idea from the main clause.

In many cases, especially in careful written French, this comma is preferred. You may sometimes see sentences without it in less formal writing, but with this structure the comma is standard and clear.

Yes, but the structure would change.

Use avant de + infinitive when French expresses the action in an infinitive form:

• Avant d'envoyer le dossier...

Use avant que + subjunctive when there is a separate subject:

• Avant que tu envoies le dossier...
• Avant qu'il envoie le dossier...

So:

• avant de + infinitive = before doing something
• avant que + subjunctive = before someone does something

In your sentence, avant d'envoyer is the simpler and more natural structure.

Yes, in many contexts enregistrer could also be used, but sauvegarder often emphasizes saving in the sense of preserving data or making sure it is kept safely.

Very roughly:

• enregistrer = to save / record
• sauvegarder = to save / back up / preserve

In computer instructions, both can appear, depending on the exact context. Sauvegarder le document strongly suggests making sure the document is saved properly before sending.

A helpful approximate pronunciation is:

Ah-vahn dahn-vwah-yay luh doh-syay, eel fo soh-veh-gar-day luh doh-kyu-mahn.

A few useful points:

• Avant: the -nt is not pronounced
• d'envoyer: the d' links directly into envoyer
• il faut: sounds roughly like eel fo
• document: the final -t is silent
• French nasal sounds in avant and document do not really exist in the same way in English, so they may take practice

It can often mean both, depending on context.

• envoyer literally means to send
• but in administrative or digital contexts, it can often correspond to submit, send off, or send in

So if this sentence appears on a website, form, or software interface, envoyer le dossier might be understood as submit the application/file rather than physically mailing something.

Context decides the most natural English interpretation.