13D Filing: Pershing Square and Automatic Data Processing Inc (ADP)

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This amendment No. 3 to Schedule 13D (this Amendment No. 3) relates
to the Schedule 13D filed on August 7, 2017 (the Original Schedule 13D, as amended and supplemented through the date of this Amendment No. 3, the Schedule 13D) by (i) Pershing Square Capital
Management, L.P., a Delaware limited partnership (Pershing Square), (ii) PS Management GP, LLC, a Delaware limited liability company (PS Management), and (iii) William A. Ackman, a citizen of the
United States of America (together with Pershing Square and PS Management, the Reporting Persons) relating to the common stock, par value $0.10 per share (the Common Stock), of Automatic Data Processing, Inc., a
Delaware corporation (the Issuer).

Capitalized terms used but not defined in this Amendment No. 3 shall have the
meanings set forth in the Schedule 13D.

Except as specifically amended by this Amendment No. 3, the Schedule 13D is unchanged.

Item 4.

Purpose of the Transaction

Item 4 of the Schedule 13D is hereby amended and
supplemented by adding the following information:

On September 15, 2017, Pershing Square sent a letter to the board of directors of
the Issuer. The letter is attached hereto as Exhibit 99.9 and incorporated by reference in this Item 4 in its entirety.

Item 5.

Interest in Securities of the Issuer

Item 5(c) of the Schedule 13D is hereby
amended and supplemented by adding the following information:

(c) Exhibit 99.2 to the Original Schedule 13D and Exhibit 99.7 to
Amendment No. 1, both of which are incorporated by reference into this Item 5(c) as if restated in full, describe all of the transactions in the Common Stock or derivatives relating to Common Stock that were effected in the past 60 days by
the Reporting Persons for the benefit of the Pershing Square Funds. Except as set forth in Exhibit 99.2, Exhibit 99.7, and as described in Amendment No. 1 with respect to the Nominee Subject Shares, no reportable transactions were effected by
any Reporting Person within the last 60 days.

Item 7.

Material to be Filed as Exhibits

Item 7 of the Schedule 13D is hereby amended and
supplemented by adding a reference to the following exhibit:

Exhibit 99.9		Letter, dated September 15, 2017.