Заявитель предъявил оригинал документа.

• заявитель is nominative singular because it is the subject.
• оригинал is accusative singular because it is the direct object of предъявил.
• документа is genitive singular because Russian says оригинал чего? = the original of what?

So the structure is basically:

[subject] + [verb] + [direct object] + [genitive complement]

Because оригинал is a masculine inanimate noun.

In Russian, for masculine inanimate nouns in the singular, the accusative form is the same as the nominative form.

So:

• nominative: оригинал
• accusative: оригинал

If it were animate, the accusative would usually match the genitive instead.

Because after оригинал Russian normally uses the genitive:

• оригинал документа = the original of the document
• копия документа = a copy of the document
• текст договора = the text of the contract

So документа answers the question чего? (of what?).

This is very common in official and formal Russian.

Предъявить is a fairly formal verb meaning something like:

• to present
• to produce
• to show for inspection

It is especially common with things like:

• documents
• passports
• IDs
• tickets
• certificates

So предъявить документ is more formal and official than simply показать документ.

Both can involve showing something, but the tone is different.

• показать = general to show
• предъявить = to present/produce officially, often because someone has the right or obligation to check it

For example:

• Покажите фотографию. = Show me the photo.
• Предъявите паспорт. = Present your passport.

In your sentence, предъявил fits the official/legal/bureaucratic style very well.

Russian past-tense verbs agree with the subject in gender and number.

Here the subject is заявитель, which is grammatically masculine singular, so the verb is:

• предъявил = masculine singular

Compare:

• заявитель предъявил = a male / grammatically masculine applicant presented
• заявительница предъявила = a female applicant presented
• заявители предъявили = the applicants presented

Предъявил is perfective, so it presents the action as completed: the applicant did present the original.

This is natural when reporting a finished official action.

Compare:

• предъявил = presented / did present (completed act)
• предъявлял = was presenting / used to present / presented at some point, with focus on process or repeated action

In a short official statement, perfective is usually the normal choice.

Not exactly.

• оригинал документа = the original of the document, as opposed to a copy
• оригинальный документ = an original/authentic document

In practice, оригинал документа is the standard official way to say that someone presented the actual original, not a copy.

Also, the adjective оригинальный can sometimes mean unusual or creative, so оригинал документа is clearer in administrative language.

Yes. Russian word order is flexible because the cases show what each word is doing.

The sentence as written—

Заявитель предъявил оригинал документа.

—is the most neutral and natural official order: subject + verb + object.

Other orders are possible, but they change the emphasis. For example:

• Оригинал документа предъявил заявитель.
  This emphasizes the original of the document or contrasts the applicant with someone else.

So the given order is the plain, neutral version.

Заявитель is a formal/official noun. Depending on context, it can mean:

• applicant
• claimant
• petitioner
• person submitting an application/request

It is common in:

• legal language
• government paperwork
• administrative forms
• immigration or registration contexts

So the whole sentence sounds quite formal and bureaucratic, which is exactly what you would expect with this vocabulary.

Russian has no articles, so there is no direct equivalent of a or the.

Whether English uses a, the, or no article at all depends on context and translation choice.

In this sentence, the context usually makes it clear that we are talking about a specific applicant and a specific document, but Russian does not mark that with separate words.

The stresses are:

• заяви́тель
• предъяви́л
• оригина́л
• докуме́нта

So the whole sentence is pronounced:

заяви́тель предъяви́л оригина́л докуме́нта