Preciso de uma fotocópia do cartão antes da reunião.

Because the verb precisar usually takes the preposition de when it means to need.

• Preciso de uma fotocópia. = I need a photocopy.
• Precisamos de ajuda. = We need help.

So in this sentence, de is required after preciso.

Here, preciso means I need.

It comes from the verb precisar:

• eu preciso = I need
• tu precisas = you need
• ele/ela precisa = he/she needs
• nós precisamos = we need

Be careful: preciso can also be an adjective meaning precise or accurate in other contexts, but here it is clearly the verb.

Because in Portuguese, de + o contracts to do.

So:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

That is why:

• do cartão = of the card
• da reunião = of the meeting / after contraction in antes da reunião

These contractions are normal and expected.

Because antes de is the usual structure for before.

Since reunião has the article a, you get:

• antes de + a reunião = antes da reunião

So:

• antes da reunião = before the meeting

Compare:

• antes de sair = before leaving
• antes do almoço = before lunch
• antes da aula = before class

Cartão is a general word meaning card. The exact meaning depends on context.

It could refer to:

• an ID card
• a bank card
• a membership card
• another official card/document

In everyday Portuguese, if the context is administrative or official, cartão often refers to some kind of identification or official card.

Yes. Fotocópia means photocopy, and cópia can also be used in many contexts.

In Portugal:

• fotocópia is perfectly normal and clear
• cópia is also common, depending on context

Sometimes people may prefer fotocópia when they want to be very specific about a paper copy made from a machine.

Yes, it is natural and correct in European Portuguese.

Possible alternatives include:

• Preciso de uma cópia do cartão antes da reunião.
• Preciso da fotocópia do cartão antes da reunião.
  This sounds more like a specific photocopy already known to both speakers.
• Pode trazer uma fotocópia do cartão antes da reunião?
  This is more polite if you are asking someone else to provide it.

Your original sentence sounds neutral and natural.

Using uma is natural because you are referring to a photocopy as a countable item.

• Preciso de uma fotocópia... = I need a photocopy...
• Preciso de fotocópias... = I need photocopies...

You can sometimes leave out the article in Portuguese, but here uma fotocópia is the most normal choice.

No, that would not be standard Portuguese.

With precisar meaning to need, you normally say:

• Preciso de uma fotocópia do cartão.

So the de is important.

The word order is very straightforward and natural in Portuguese:

• Preciso = I need
• de uma fotocópia = a photocopy
• do cartão = of the card
• antes da reunião = before the meeting

So the structure is basically:

[verb] + [de + thing needed] + [extra detail] + [time expression]

Portuguese often uses this kind of order, and it matches English fairly closely here.

In European Portuguese, reunião is pronounced approximately like reh-oo-nee-OWng, though the final sound is nasal.

A few points:

• reu- is not like English roo exactly; it is more compact
• -ni- is clear
• -ão is a very common nasal ending in Portuguese

That final -ão appears in many words:

• cartão
• reunião
• informação
• situação

For English speakers, the hardest part is usually making the final vowel nasal rather than pronouncing a full ow sound.

Because both end in -ão, which is a very common Portuguese ending.

This ending is usually nasal and often corresponds to different endings in English or other Romance languages. For learners, the important thing is to recognize it as a frequent pattern.

Examples:

• cartão = card
• reunião = meeting
• avião = airplane
• informação = information

It is one of the most recognizable sound patterns in Portuguese.

Literally, it is a statement: I need a photocopy of the card before the meeting.

But in real life, it can function indirectly as a request, depending on tone and context. For example, if you say it to someone who is expected to provide the photocopy, it may sound like an implied request.

If you want to sound more directly polite, you could say:

• Pode trazer uma fotocópia do cartão antes da reunião?
• Preciso que me envie uma fotocópia do cartão antes da reunião.

So your sentence is grammatically a statement, but pragmatically it can also suggest a request.

Usually, yes, slightly.

• fotocópia sounds more specific and a bit more administrative
• cópia is more general and can refer to many kinds of copies

In offices, schools, and official situations in Portugal, fotocópia is very common and sounds completely natural.