The Book of Fatimah is the name of the book that the divine angel explained to Hazrat Fatimah (pbuh) and Imam Ali (pbuh) wrote them. The contents of this book include the position of the Prophet (PBUH) in heaven and future events. This book was with the Shia imams and it was passed from hand to hand and others did not have access to this book and do not have it. This book is now in the hands of Imam Zaman (AS). Some Sunnis have claimed that Shiites have another Qur'an called Mushaf Fatimah, but Shia imams have always emphasized that this Mushaf is a book other than the Qur'an and Shiites accept the same Qur'an common among Muslims.
The descent of the divine angel and God's communication with non-prophets is possible through angels and revelation; As the verses talk about the relationship between the angel and Maryam (pbuh) or that everyone agrees that the mother of Prophet Moses (pbuh) was inspired to throw her child into the river.