The FAQ doesn't address it completely in my opinion.
> Many people believe PDF to be “impossible to edit,” but beware: minor edits in PDFs, such as swapping figures on an invoice, are trivial — therefore you need other technologies, such as digital signatures, to verify that your PDFs have not been tampered with.
That's not really the point that it can't be edited, the value to me is that the sender has confidence that it will look the same to the receiver as the sender.
And then of course there is the deliberately edit hostile way that PDFs can be (ab)used, by printing a document and then scanning it to PDF. In my experience some lawyers like this because it means that to suggest edits you have to retype or OCR entire paragraphs
I used to do a variation of this by converting all text to outlines in a PDF. It will even deter more people from editing the document. This also saves paper, and text will remain sharp (although slightly different because operating systems have different heuristics when it comes to rasterizing text and graphics).
> That's not really the point that it can't be edited, the value to me is that the sender has confidence that it will look the same to the receiver as the sender.
Different PDF reader software, and even sometimes the same reader software installed in different environments, can render PDFs, especially those containing any text differently.
If you want confidence that it will appear the same, pure image formats are a safer bet.
> Many people believe PDF to be “impossible to edit,” but beware: minor edits in PDFs, such as swapping figures on an invoice, are trivial — therefore you need other technologies, such as digital signatures, to verify that your PDFs have not been tampered with.
That's not really the point that it can't be edited, the value to me is that the sender has confidence that it will look the same to the receiver as the sender.