ENH: Add command to export annotations as JSON

[MartinThoma]

This was originally asked in py-pdf/pypdf#2291

Proposed syntax:

$ pdfly annotations export
[
{"page_index": 0, "/Subtype": }
]

So essentially the idea is to export the same as defined in 12.5 Annotations (PDF 1.7 specifications), but add the "page_index" to the dictionary.

For the moment, we would only support the JSON export. If we want to add more export formats, we can add --format with a default value of JSON.

[mah-emad]

Hi Martin,
basically I have a pdf stored in a database and follows a workflow across multiple specialties, each will put comments on the pdf and in the end sign it.
what i'm trying to do is export only the comments/signatures and save it to the database instead of saving the whole PDF again.

I tried pikepdf (which is bindings to qpdf) and I can export the whole document to JSON and through Deepdiff store only the difference and apply the patch later.
and I can always compare the 2 pdfs on the binary level with bsdiff4 and store the difference without converting to JSON first.

[MartinThoma]

You can export the annotations like this:

from pypdf import PdfReader
import json

reader = PdfReader("annotated_pdf.pdf")

annotations = []
for page_index, page in enumerate(reader.pages):
    for annotation in page.annotations:
        annotations.append({"page_index": page_index, **annotation})

print(json.dumps(annotations, indent=4))  # ìndent=None` for a one-line export

I'm not sure yet if adding this to pdfly is useful for others, but at least it would solve your issue of exporting the annotations.

Importing the annotations from JSON to a PDF is a different topic.

When you want to have cryptographic sigantures you should save multiple versions of that file. Or the latest file as it will contain all of the revisions.

[mah-emad]

Hi Martin,
Thanks for your reply, when i try the code it fails with the following:
annotations.append({"page_index": page_index, **annotation}) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TypeError: 'IndirectObject' object is not a mapping

any thoughts how to handle importing back annotations

[pubpub-zz]

Hi Martin, Thanks for your reply, when i try the code it fails with the following: annotations.append({"page_index": page_index, **annotation}) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TypeError: 'IndirectObject' object is not a mapping

any thoughts how to handle importing back annotations

try :

annotations.append({"page_index": page_index, **(annotation.get_object())})

[mah-emad]

now the error is
TypeError: Object of type IndirectObject is not JSON serializable

i guess the problem is with the internal custom types. that will require mapping all your types to pure python types before trying to serialize