Extend piece of writing with publicist's introduction (8)
I believe the answer is:
protract
'extend' is the definition.
(synonyms)
'piece of writing with publicist's introduction' is the wordplay.
'piece of writing' becomes 'tract' (I've seen this before).
'with' means one lot of letters go next to another.
'publicist's introduction' becomes 'pro' (I can't justify this - if you can you should give a lot more credence to this answer).
'tract' after 'pro' is 'PROTRACT'.
Can you help me to learn more?
(Other definitions for protract that I've seen before include "Extend length" , "Draw out, prolong" , "Stretch out" , "Drag out at length" , "Increase" .)