If someone sends me a document with text in it that they meant to remove but didn't and then I read that text, I haven't hacked anything they're just incompetent.
Hacking is unauthorised use of a system. Reading a document that was not adequately redacted can hardly be considered hacking.
Precisely. If someone wants me to sign a contract on acceptable use of resources (like an agreement not to reverse engineer their software) they send me then that's another thing.
Absent that excluding other default protections like copyright, what I do with it should fall under the assumption of "basically anything".
If this were prior to 2021, I would say the CFAA could be violated so long as the property owner's _intentions_ were for that information to only be accessible to certain users. But I think the CFAA has been sufficiently reduced in scope after Van Buren v United States [0]
[0] https://en.wikipedia.org/wiki/Van_Buren_v._United_States
Hacking is not just authorised use of a system. Hacking and hacking techniques can apply to systems you fully own or systems which you are authorised to hack. Hacking is using something in a way that the designer didn’t anticipate or intend on.
Adobe designed pdf to behave this way. Placing layers over text doesn’t remove the text from the file. They have a specific redaction feature for that purpose.
Or in case some folks find the addition of a computer confusing here, if someone sends you a physical letter and they've used correction tape or a black marker to obscure some parts of the letter, and you scratch away the correction tape or hold the letter up to a light source to read what's underneath, have you committed a crime?
I'm not a lawyer, so I don't know what the law has to say about this. But I do have at least a small handful of brain cells to rub together, so I know what the law _should_ say about this.