E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
said to be from Pamphila, a Greek lady, whose chief work is a commonplace book of anecdotes, epitomes, notes, etc. Dr. Johnson suggests par-un-filet (held by a thread)i.e. stitched, but not bound; another derivation is pagin filat (pages tacked together). It was anciently written panfletus, pamflete, and by Caxton paunflet.