Silent modification of a document
<p>From time to time one is presented with adhesion contracts which have not been signed by the presenting party, and contain terms which are unpalatable.  </p>

<p>Were one to modify the contract in ways which may not be picked up by the other party prior to signing it to make it more equitable/favourable to oneself prior to returning the document,  and without drawing the other parties attention to the changes, would one be acting illegally ?</p>

<p>I'd be interested in any specific laws which might cover this for a particular jurisdiction, but I'm more interested in any underlying basis in law why this behaviour would be considered illegal.    (One thought is breach of copyright, but I'm not sure if that could be applied)</p>

<p>Changing the document is perfectly legal, this is called negotiation.</p>

<p>Deliberately hiding that you changed the document would make any contract formed on that basis void and, depending on who and where you are could put you in breach (and liable to prosecution) of consumer protection laws.</p>

<p>Copyright exists in the document (jointly if you both authored it), however, using it for the purpose of giving effect to the contract would be (implicitly) licensed. Of course, you couldn't use their document as the basis of a contract between you and a third party.</p>

adhesion-contracts