令 as a classifier is a printing-and-paper-trade term loaned from English 'ream' — 500 sheets of flat-stock paper. You will see it on supplier invoices and in factory orders but almost never in everyday speech, where people count paper by 张 (sheet) or 包 (pack) instead.
mistakes
Same character, different tone. The everyday command sense is 令 (4th tone); the ream classifier is 令 (3rd tone). Hearing 'three lǐng' in a paper-mill context means three reams, not three orders.
Top person radical (Kangxi #9), drawn as a wide roof. The ream-classifier reading is a 20th-century loan from English 'ream' borrowed phonetically into the existing graph; the radical structure is shared with the dominant lìng reading and does not contribute to this paper-trade meaning.
Bottom kneeling-person component (standalone 卩). Inherits its shape from the lìng (command) reading; carries no extra meaning for the lǐng (ream) sense, which was attached to this graph as a phonetic loan from English 'ream' in the paper trade.
