It's a lot more subtle than that. I wrote the MDP code for Adobe Acrobat
9 (June 2008). Certainly there are the obvious changes: something in a
content stream changed, but then there are less obvious changes
(appearance string changes for annotations that are locked). One which I
just ran into is a MarkInfo dictionary in the latest incremental save
that is identical to the MarkInfo dictionary in the previous save. The
fact that it is in the latest incremental save triggered the change
notice. Back when I had access to Acrobat source code I could debug and
discover what was being changed. But that was many years ago and I don't
know what modifications to the original code have been made. It's my own
fault for not spitting more detailed debug information, I guess, but
that's 15 years ago.
MDP analysis is between a signed version and subsequent versions,
pairwise. Not every change is invalidating.
On 10/6/2023 9:43 PM, John Lussmyer wrote:
I doubt there is a way.
It's most likely that the signing code makes a MD5 checksum (or
similar) of the file when it is signed.
If the file is changed, checking the signing will re-calculate the
checksum and find that it is different. There isn't any info on what
changed, just that SOMETHING changed.
On 10/6/2023 8:50 PM, Tilman Hausherr wrote:
On 06.10.2023 19:50, Marc Kaufman wrote:
I find myself debugging PDF files where Acrobat claims "Document has
been altered or corrupted since it was signed." I would dearly love
to see which objects belong to the last xref (color code is OK). Has
anyone added that feature to PDF Debugger, or know where I can find
one? Just comparing revisions is not enough, since sometimes the
"changed" object is identical to the same object in the previous
revision.
I don't know of any. I research such questions the hard way, with
NOTEPAD++.
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