En la oficina me pidieron el expediente completo antes de aceptar la solicitud.

Because pedir often works like to ask someone for something.

In Spanish, the person being asked is usually marked with an indirect object pronoun:

• Me pidieron el expediente = They asked me for the file
• Literally, something like They requested the file from/to me

So in this sentence:

• me = to me / from me
• el expediente completo = the thing requested

A useful pattern is:

pedir algo a alguien = to ask someone for something

So:

• Me pidieron el expediente = They asked me for the file
• Le pidieron ayuda = They asked him/her for help

Pidieron is third person plural preterite: they asked/requested.

Spanish often leaves out the subject pronoun, so instead of saying ellos pidieron, it simply says pidieron.

In this sentence, the idea is something like:

• En la oficina me pidieron... = At the office, they asked me...

That they does not have to refer to a specific named group. It can mean:

• the staff
• the people in the office
• whoever was handling the process

This is very common in Spanish.

Pidieron is the preterite of pedir.

It is used because the sentence refers to a completed action in the past: they asked for the file before another action happened.

So:

• me pidieron = they asked me / they requested

The preterite fits because it presents the request as a finished event.

If you used the imperfect instead:

• me pedían

that would suggest something more ongoing, habitual, or backgrounded, such as:

• they kept asking me
• they used to ask me
• they were asking me

But here the sentence points to one completed step in a process, so pidieron is the natural choice.

Both are possible in English, depending on tone.

In this sentence, pedir means to ask for or to request.

That is important because pedir is not the same as preguntar.

• preguntar = to ask a question
• pedir = to ask for something

Examples:

• Pregunté la hora is not natural Spanish
• Pregunté qué hora era = I asked what time it was
• Pedí ayuda = I asked for help
• Me pidieron el expediente = They asked me for the file

Because el expediente completo is a thing/document being requested, pedir is exactly the right verb.

En la oficina means in the office or at the office, depending on context.

Here it sets the scene: it tells you where this happened.

• En la oficina = at/in the office

A native English speaker might wonder why it is not a la oficina, but that would mean movement to the office.

Compare:

• En la oficina me pidieron... = At the office, they asked me...
• Fui a la oficina = I went to the office

So en is used because the speaker is locating the action, not expressing movement toward the office.

Expediente is a formal word. In Spain, it often means a file, case file, record, or dossier containing documents related to a person, case, application, or procedure.

So el expediente completo suggests:

• the full file
• all the paperwork
• the complete set of documents on record

It sounds administrative and bureaucratic, which fits very well with:

• la oficina
• la solicitud

This is more formal than a general word like papeles.

In Spanish, adjectives usually come after the noun:

• el expediente completo
• la solicitud oficial
• el documento necesario

So expediente completo is the normal order.

Also, completo agrees with expediente:

• expediente is masculine singular
• so the adjective is completo

If the noun were feminine plural, for example:

• las solicitudes completas

the adjective would change too.

Putting the adjective before the noun can sometimes happen in Spanish, but it often sounds literary, emphatic, or changes the nuance. Here, el expediente completo is the natural and standard choice.

Because Spanish commonly uses:

antes de + infinitive

when the subject is the same as the subject of the main clause, or when the subject is understood from context.

Here:

• me pidieron el expediente completo
• antes de aceptar la solicitud

The understood subject of aceptar is the same people as the one implied by pidieron: the office staff / the people handling the application.

So the meaning is:

• they asked me for the complete file before accepting the application

This is very natural Spanish.

Use antes de + infinitive when there is no new explicit subject, or when the subject is the same and understood.

Use antes de que + subjunctive when a different subject is introduced.

Compare:

• Me pidieron el expediente antes de aceptar la solicitud.
  = They asked me for the file before accepting the application.
  (same understood subject: they)

• Me pidieron el expediente antes de que yo presentara la solicitud.
  = They asked me for the file before I submitted the application.
  (different subject: yo)

So in your sentence, antes de aceptar is used because Spanish does not need a separate clause there.

Because Spanish often uses the definite article where English might use a possessive or just leave it implicit.

• la solicitud = the application / the request

This usually means the application already known in the context.

Depending on the situation, it may well be my application, but Spanish does not always need to say mi if it is obvious whose application it is.

So:

• antes de aceptar la solicitud sounds perfectly natural
• antes de aceptar mi solicitud is also possible if you want to make it explicitly personal

The version with la solicitud sounds a bit more neutral and administrative.

Yes.

Solicitud is a formal noun and can mean:

• request
• application

Which translation is best depends on context.

In an office or administrative setting, solicitud very often means application, for example:

• a benefits application
• a permit application
• an enrolment application

In other contexts, it may simply mean a formal request.

Because the sentence also includes expediente and oficina, many learners would naturally understand solicitud here as something like an official application.

Because unstressed object pronouns in Spanish usually go before a conjugated verb.

So:

• me pidieron
• te dijeron
• le entregaron

This is standard word order.

With an infinitive, gerund, or affirmative command, pronouns can attach to the end instead:

• aceptar la solicitud
• aceptarla = to accept it

So your sentence could also contain a structure like:

• antes de aceptarla

where la refers to la solicitud.

That is a useful pattern to notice:

• me pidieron = pronoun before a conjugated verb
• aceptarla = pronoun attached to an infinitive

Yes. Spanish allows fairly flexible word order, especially with time and place expressions.

For example, these are all natural:

• En la oficina me pidieron el expediente completo antes de aceptar la solicitud.
• Me pidieron el expediente completo en la oficina antes de aceptar la solicitud.
• Antes de aceptar la solicitud, en la oficina me pidieron el expediente completo.

The original version is very natural because it starts by setting the location:

• En la oficina...

That helps frame the whole situation immediately.

So the word order is not random, but it is also not the only possible order.