Phoned-in document (3)
I believe the answer is:
fax
'phoned-in document' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fax that I've seen before include "Means of communication" , "Transmit document" , "Modern method of transmitting printed matter by phone" , "Transmission of exact copies of documents electronically" , "Electronic transmission" .)