"to steal in small quantities" (intrans.); "to steal or gain by petty theft" (trans.), 1540s, from pilfer (n.) "spoils, booty," c. 1400, from Old French pelfre "booty, spoils" (11c.), a word of unknown origin, possibly related to pelf. Related: Pilfered; pilfering. Pulfrour "a thief" is attested from mid-14c., implying earlier use.
word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).
<a href="https://www.etymonline.com/word/pilferage">Etymology of pilferage by etymonline</a>
Harper, D. (n.d.). Etymology of pilferage. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/pilferage