Sem a fotocópia do documento, o formulário fica inválido.

Yes. Sem means without, and it introduces the condition that is missing: sem a fotocópia do documento.

It is completely normal to put that phrase first. In Portuguese, starting with a condition or circumstance is very common, especially in instructions, warnings, and official language. It gives emphasis to the missing requirement.

A more neutral word order would be:

O formulário fica inválido sem a fotocópia do documento.

Both are correct.

Using a fotocópia makes it sound like a specific, expected photocopy: the photocopy that is required for this document/process.

If you said uma fotocópia, the meaning would be more like any photocopy or a photocopy in a less specific sense.

In administrative Portuguese, the definite article is very common when referring to required documents, even where English might prefer a:

• Sem a fotocópia do documento...
• Sem a assinatura...
• Sem o comprovativo...

So this sounds very natural.

Because de contracts with the definite article, but sem normally does not.

So:

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

That is why de o documento becomes do documento.

But with sem, standard Portuguese keeps the words separate:

• sem o passaporte
• sem a fotocópia
• sem os anexos

So sem a is correct, not a contraction.

The comma separates the introductory phrase from the main clause.

The first part, Sem a fotocópia do documento, sets the condition. The second part, o formulário fica inválido, gives the result.

In Portuguese, a comma is very common when a fairly long introductory phrase comes first. It helps readability and sounds natural in written language, especially formal writing.

Without the comma, the sentence is still understandable, but the version with the comma is better.

Here, fica does not mean stays in the literal sense. It means something like becomes, ends up, or is rendered.

Portuguese ficar is a very flexible verb. Depending on the context, it can mean:

• to stay
• to be located
• to become
• to end up

In this sentence, it expresses a resulting state:

• because the photocopy is missing, the form becomes / is considered invalid.

Fica inválido emphasizes the result of a condition not being met.

It suggests:

• if the photocopy is not included,
• then the form becomes invalid / is treated as invalid.

If you said é inválido, that would sound more like a plain statement of fact:

• O formulário é inválido sem a fotocópia do documento.

That version is also possible, but fica inválido is especially common in bureaucratic or administrative language because it highlights the consequence.

Here it means not valid, not acceptable, or not legally/administratively valid for processing.

It does not usually mean illegal in this context. It means the form will not count as properly submitted or acceptable if that document is missing.

So this is typical office or official language: the form is not valid for the procedure unless the required photocopy is attached.

Because the adjective agrees with o formulário, which is masculine singular.

In Portuguese, adjectives usually match the noun in gender and number:

• o formulário inválido — masculine singular
• a ficha inválida — feminine singular
• os formulários inválidos — masculine plural
• as fichas inválidas — feminine plural

Since the subject is o formulário, the correct form is inválido.

Yes, absolutely.

That version is perfectly correct: O formulário fica inválido sem a fotocópia do documento.

The difference is mainly one of emphasis:

• Sem a fotocópia do documento, o formulário fica inválido.
  Emphasizes the missing requirement first.
• O formulário fica inválido sem a fotocópia do documento.
  Starts with the form itself and then adds the condition.

The first version sounds especially natural in warnings, notices, and instructions.

Not always, though they can overlap.

Fotocópia specifically means a photocopy, usually a paper copy made from a machine.

Cópia is broader and can mean:

• a copy in general
• a paper copy
• sometimes even a digital copy, depending on context

In official Portuguese from Portugal, fotocópia is very common when the administration wants an actual photocopy of a document. If they wrote cópia, the meaning could be slightly broader.

In normal, complete Portuguese sentences, yes, they are very natural and usually expected.

Portuguese uses definite articles more often than English does. So where English might say:

• Without a photocopy of the document, the form is invalid

Portuguese naturally says:

• Sem a fotocópia do documento, o formulário fica inválido.

You might see articles omitted in headings, forms, or note-style language, for example:

• Formulário inválido sem fotocópia do documento

But in a full sentence, the version with articles sounds more standard and natural.

Yes, very natural.

It sounds like the kind of sentence you could see in:

• application instructions
• public administration notices
• form submission rules
• document checklists

The structure is very typical of formal Portuguese from Portugal: a condition first, then the consequence. The phrase fica inválido is also very common in administrative language.

A slightly more formal alternative could be:

• Sem a fotocópia do documento, o formulário será considerado inválido.

But the original sentence is already perfectly natural.