The most common and most likely answer to this crossword clue is the 5 letter word RECTO
I've seen this crossword clue in Financial Times
R
E
C
T
O
More clues leading to the result RECTO
- Right page in incorrect order?
- One page coming out of directory
- Senior academic ignoring last page in book
- Read this page in correct order?
- College head, finishing early, leaves to the right
- Page priest: his second run out
- Page Three, perhaps, right to be hidden from vicar
- Play area closed -- leaves to the right
- Page in directory
- Cleric doesn’t finish first page of book
Buddy explains!

The straight part
We know that "first page of book" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case first page of book = recto.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RECTO mean?
RECTO noun- The front side of a flat object which is to be examined visually, as for reading, such as a sheet, leaf, coin or medal.
- The right-hand page of a book of a script which reads from left to right, usually having an odd page number.
- A writ of right.