Green’s Dictionary of Slang

a pickpocket.

1659		Catterpillers of this Nation Anatomized 2: The Filer or Cloyer (alias) a common Thief.
c.1661		A Beggar I’ll Be in Farmer Musa Pedestris (1896) 26: A Craver my Father, a Maunder my Mother, / A Filer my Sister, a Filcher my Brother, / A Canter my Unkle, that car’d not for Pelf, / A Litter my Aunt, and a Beggar my self.
1674		C. Cotton Compleat Gamester 6: Shoals of Huffs, Hectors, Setters, Gilts, Pads, Biters, Divers, Lifters, Filers, Budgies, Droppers, Crossbyters, etc., and these may all pass under the general and common apellation of Rooks.
1693		Poor Robin n.p.: A most plentiful crop [...] of hectors, trepanners, gilts, pads, biters, prigs, divers, lifters, filers, bulkers, droppers, famblers, donnakers, cross-biters, kidnappers, vouchers, millikers, pymers, decoys, and shop-lifters, all Newgate-birds, whom the devil prepares ready fitted for Tyburn, ready to drop into the hangman’s mouth [N].
1719		in D’Urfey Pills to Purge Melancholy III 100: A Filer my Sister, a Filcher my Brother.
1734		C. Johnson Hist. of Highwaymen &c. 24: His Fraternity being thus composed of Lifters, Pickpockets, and Filers.
1749		Caledonian Mercury 21 Mar. 1/1: Backwards rode Filch, who Pockets us'd to rifle, / And thought it hard to hang for such a trifle. / There having been no Pickpokets executed since the Guinea-filers.
1754		‘The Beggar’ Muses Delight 133: A craver my father, a maunder my mother, / A filer my sister, a filcher my brother.
1897		C. Whibley ‘Moll Cutpurse’ in Book of Scoundrels 59: She is remembered [...] not only as the Queen Regent of Misrule, the benevolent tyrant of cly-filers and heavers.