Learn Spanish (Latin America): Había leído la biografía de la mujer cuya herencia compartimos. - I had read the biography of the woman whose heritage we share.

The word for 'whose' (cuyo, cuya, cuyos, cuyas) is a relative possessive adjective. Unlike in English, it agrees in gender and number with the thing being possessed, not the owner! Here, it matches the possession, herencia (feminine, singular), so it becomes cuya.

What tense is Había leído and how is it formed?

This is the past perfect tense. It translates to 'had read'. You form it by combining the imperfect tense of the helping verb haber (here, había) with the past participle of the main verb (leído).

How do we know Había leído means 'I had read' when it could also mean 'he had read' or 'she had read'?

On its own, había leído can apply to 'yo', 'él', 'ella', or 'usted'. The correct subject is usually obvious from the wider context of the conversation. If it were ambiguous in real life, you would simply add the pronoun for clarity, such as Yo había leído.

Why does leído have an accent mark on the letter 'i'?

The accent mark breaks what would otherwise be a diphthong (two vowels blending into one syllable). Without the accent, the 'e' and 'i' would blend together. The accent ensures the word is pronounced as three distinct syllables (le-í-do).