I have a PDF to send to someone, but I'd like to be pretty sure they can't change it. Are there any easy solutions to this? Encrypting it is likely to be too much work.
It's going to be a scan, not saving to PDF from a webpage, Word document, etc.
If it's a scan, then it's likely already an image. That precludes the easy method of editing (editing text).
But once it's on someone else's computer, you cannot completely prevent it from being modified. What if they simply take screen captures and modify those?
The best you can do is make it non-trivial.
You can set a password within the PDF capture program, but unfortunately those are easy to overcome.