Learn Spanish (Latin America): Quiero que el documento sea válido.

The phrase Quiero que (I want that) expresses a desire about something else, which triggers the subjunctive mood. sea is the irregular present subjunctive form of ser (to be) for a third-person subject like el documento.

Why can't I just use the infinitive ser like in the English phrase 'I want the document to be'?

In English, we use an infinitive structure like 'I want the document to be valid'. In Spanish, when the person wanting the action is different from the person or thing doing the action, you must use que plus a conjugated subjunctive verb. It literally translates to 'I want that the document be valid'.

Why does this sentence use a form of ser instead of estar?

We use ser because being valid is an inherent, defining characteristic of the document's official status. We use estar for temporary states, emotions, or physical locations.

Why does the word válido have a written accent mark?

The spoken stress in válido falls on the third-to-last syllable (vá-li-do). In Spanish, any word with the stress on the third-to-last syllable must always have a written accent mark to show you where to place the emphasis.