De haber leído el albarán, habría notado el desperfecto.

In this sentence, de haber leído means if he/she had read.

It is a compact, somewhat formal way of expressing a past unreal condition. The fuller version would be:

Si hubiera leído el albarán, habría notado el desperfecto.

So:

• de haber leído = if having read / had they read
• natural English translation = if he/she had read

They usually do. The most common way to say this is with si:

• Si hubiera leído el albarán, habría notado el desperfecto.

But Spanish also has a more literary, formal, or concise structure:

• De + infinitive / de + haber + past participle

So:

• De haber leído... = If he/she had read...
• De saberlo... = If I had known that...

This de structure is less common in everyday conversation than si, but it is perfectly correct and often found in writing or more formal speech.

Because the sentence refers to something that did not happen in the past.

• leer = to read
• haber leído = to have read

The form haber + past participle expresses a completed action. Here, the idea is:

• first, reading the delivery note would have happened
• then, noticing the damage would have happened

So de haber leído specifically means if he/she had read, not just if he/she read.

Habría notado is the conditional perfect.

It is used here because the sentence is talking about a result that would have happened, but in fact did not happen.

So the structure is:

• De haber leído el albarán = if he/she had read the delivery note
• habría notado el desperfecto = he/she would have noticed the damage

This is a standard pattern for past unreal situations in Spanish:

• condition that did not happen
• result that would have happened

Spanish often leaves the subject pronoun out because the verb form already gives enough information.

In habría notado, the subject could be:

• él = he
• ella = she
• usted = you (formal)

Without context, the sentence is ambiguous. Spanish is very comfortable with that. The surrounding context usually makes it clear who is meant.

Yes, absolutely. That version is probably the one most learners will hear and use most often.

• De haber leído el albarán, habría notado el desperfecto.
• Si hubiera leído el albarán, habría notado el desperfecto.

Both are correct and mean the same thing.

In general:

• si hubiera leído... = more common and neutral
• de haber leído... = more formal, condensed, or literary

In Spain, albarán usually means a delivery note or delivery slip: a document that accompanies goods and lists what has been delivered.

It is not exactly the same as:

• recibo = receipt
• factura = invoice

So in this sentence, the idea is probably that if the person had checked the delivery document, they would have noticed that something was damaged or wrong.

Desperfecto means a defect, damage, or problem in the condition of something, especially a physical flaw or damage.

It overlaps with daño, but there is a slight nuance:

• daño is a broad word for damage or harm
• desperfecto often refers to a visible flaw, defect, breakage, or damaged state in an object

So here el desperfecto suggests something like:

• the damage
• the defect
• the flaw

For example, a dent, crack, scratch, or broken part.

Because leído is the past participle of leer, and the accent shows that the vowels are pronounced in separate syllables:

• le-í-do

Without the accent, Spanish pronunciation rules would not represent the word correctly.

This happens with some verbs whose stem ends in a vowel:

• leer → leído
• oír → oído
• caer → caído

So the accent is an important part of the spelling.

Yes, slightly.

The combination de haber leído... sounds more formal, written, or polished than the more everyday si hubiera leído... structure.

That does not mean it is unnatural. It is just less conversational. You might see it in:

• reports
• formal explanations
• written complaints
• journalistic or literary prose

A more everyday spoken version would usually be:

• Si hubiera leído el albarán, habría notado el desperfecto.

Yes. The structure itself does not change for person, because the subject is usually understood from context or from the main clause.

For example:

• De haberlo sabido, habría ido. = If I had known, I would have gone.
• De haber llegado antes, habríamos comido juntos. = If we had arrived earlier, we would have eaten together.

So de haber + past participle works as a general conditional structure for past unreal situations. The subject is usually identified by the verb in the main clause or by context.

Yes, notar is a very good match here.

In this context:

• notar = to notice
• darse cuenta de = to realize

Both can sometimes work, but they are not identical.

• notar el desperfecto focuses on perceiving or spotting the defect
• darse cuenta del desperfecto focuses a bit more on becoming aware of it

So habría notado el desperfecto naturally means would have noticed the damage/defect.