Don't you need a contract in the first place for it to be an amendment? It can't be a contract if the signer rewrote the terms and gave it back to you first without your guy accepting it. And I can't see how that acceptance would be a mistake except if failure to read the terms offered was actually legitimate grounds to argue mistake.
Edit: this is a fascinating topic for me...never come across people who try to change form contracts on the spot this way
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You've been here this long and you're surprised one of us would do so?
I'm more surprised people think PDFs can't be altered so they don't even think about it. Another wrinkle of theoretical interest is if the PDF was 'protected' (BWAHAHA) by a proprietary scheme. People are weird enough to think if a vendor says "secure" or "protected", they actually mean it.
I'd never sign a non-compete that didn't include $$ if I was blocked from a job as a result. NDA's are fine. Got no issue with them.
We had an accountant at one time that told us he'd gotten back into accounting after a 10 year hiatus due to a NCA. He didn't mind that hiatus as he was well compensated for it, and had another effective career for that time period to boot.
I've love to know that story. 10 year compensated hiatus would be... amazing. Even at a fraction of my current pay. Writing, travel, you name it.