halacha - Publisher prohibiting purchaser from sharing

Tradition articles are downloadable from the Tradition Online website, which prohibits further distribution of the materials. On each download page there is the following warning:

It is strictly forbidden for both subscribers and article purchasers to share article downloads with others.

On what basis does the magazine (or the RCA, which publishes the magazine) retain such a right to prohibit any type of sharing? Surely even Copyright Law allows the purchaser of a published work to share it with others.

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To clarify, my question is whether that statement is:

1. reflective of law and therefore Halachah;


2. effective of Halachah (like a sale 'Al Tenai, or a Neder, perhaps?); or


3. meaningless.