[whenc]

You can do:

  cpdf -output-json in.pdf -o out.json

(Modify out.json as liked)

  cpdf -j out.json -o out.pdf

(Disclaimer, I wrote it.)

[whizzter]

Seems cool for document usage, the online JS version however thrashed the digital signatures with that rotate 10 degrees demo (not entirely if it was just a checksum issue but it seemed to be worse as in tinkering with or not roundtripping the signature data object).