Presentamos la documentación acreditativa en la sede electrónica.

Presentamos is the first-person plural form of presentar.

It can mean either:

• we present / we submit (present tense), or
• we presented / we submitted (preterite)

So, by itself, presentamos is ambiguous. In a real context, the surrounding sentence or situation tells you which meaning is intended.

This happens with some -ar verbs in Spanish: the nosotros form is the same in the present and the preterite.

Spanish often omits subject pronouns because the verb ending already shows who the subject is.

• presentamos = we present / we submitted

So nosotros is usually unnecessary unless you want to:

• add emphasis
• create contrast
• avoid confusion

For example:

• Nosotros presentamos la documentación, no ellos.
  We submitted the documents, not them.

In the original sentence, leaving out nosotros sounds natural.

In everyday Spanish, presentar can mean to present, but in administrative or legal contexts it often means:

• to submit
• to file
• to hand in

So in this sentence, presentamos la documentación is best understood as we submitted/filed the documentation, not we gave a presentation.

Documentación is a collective or uncountable noun here. It refers to the set of documents required for a procedure.

So:

• la documentación = the documentation / the paperwork
• los documentos = the documents

Spanish administrative language very often uses documentación because it sounds formal and refers to the whole package of required papers, not just individual items.

Acreditativa is an adjective meaning something like:

• supporting
• proving
• certifying
• that serves as proof

So la documentación acreditativa means the supporting documentation or the documentation that proves something.

It comes from the verb acreditar, which means to prove, to certify, or to accredit, depending on context.

Because it has to agree with documentación, which is:

• singular
• feminine

So the adjective must also be singular feminine:

• documentación acreditativa

If the noun were masculine, you would use acreditativo.
If it were plural, the adjective would also become plural.

In Spanish, adjectives often come after the noun, especially when they are:

• descriptive
• technical
• classificatory
• formal or administrative

So documentación acreditativa is the normal word order.

Putting the adjective before the noun would usually sound unusual here and might change the tone or emphasis.

In Spain, sede electrónica is a very specific administrative term. It means the official online portal of a public body or institution, where you can do formal procedures such as:

• submitting documents
• checking notifications
• filing applications
• downloading certificates

So it is not just any website. It refers to the official electronic office/portal used for government or institutional procedures.

Because en is used here to express the place or medium where the submission happens.

• presentar algo en la sede electrónica = to submit something through/on the electronic office portal

Using a would not sound right in this context.

Think of en here as meaning:

• in
• on
• through, depending on how naturally you translate it

In administrative Spanish, en la sede electrónica is the standard expression.

Spanish uses definite articles more often than English.

• la documentación refers to the specific documentation relevant to the procedure
• la sede electrónica refers to the official electronic portal being used

Even where English might say supporting documentation or submitted online, Spanish often keeps the article:

• la documentación
• la sede electrónica

This is completely natural in Spanish.

Yes, sede is a feminine noun:

• la sede

Not all feminine nouns end in -a, and not all nouns ending in -e are masculine. Gender has to be learned noun by noun in many cases.

Here that is why you get:

• la sede
• la sede electrónica

with the adjective also in feminine form: electrónica.

Yes, very much so. The sentence is typical of administrative Spanish in Spain.

Several things make it sound formal:

• presentamos used in the sense of submit/file
• la documentación
• acreditativa
• la sede electrónica

In everyday conversation, a speaker might say something simpler, depending on context, such as:

• Subimos los documentos a la web oficial.
• Enviamos los papeles por la sede electrónica.

But the original sentence sounds exactly like the kind of wording you would see in a form, official email, or government procedure.