In a book, end of paragraph penned (2,4)
I believe the answer is:
at home
'in' is the definition.
(someone at home is 'in')
'a book end of paragraph penned' is the wordplay.
'book' becomes 'tome' (a tome is a book).
'end of' indicates one should take the final letters.
'penned' indicates putting letters inside (inserted letters are enclosed or penned in).
The last letter of 'paragraph' is 'h'.
'tome' enclosing 'h' is 'thome'.
'a'+'thome'='AT-HOME'
(Other definitions for at home that I've seen before include "In (for a party?)" , "Comfortable - in one's own country" , "Oh mate! (anag)" , "Reception in one's own abode" , "In one's own house" .)