ODP: hidden slides are exported as normal content #4765

Bug

A slide that is hidden in an OpenDocument presentation is converted like a normal slide. Its title and text go into the body of the document and into the Markdown export, although the slide is not presented.

ODF marks a hidden slide on the slide's style: <style:drawing-page-properties presentation:visibility="hidden"/>. The ODP slide loop in OdpDocumentBackend.convert does not read it. The same backend already sends hidden ODS sheets (table:display="false") to ContentLayer.INVISIBLE, and #4647 / #4733 did the same for hidden PowerPoint slides and shapes.

Steps to reproduce

The attached Test_ODP.odp was exported from Google Slides (File → Download → ODP Document) with slide 2 set to Skip slide. In the file, slide 2 uses style dp3, which has presentation:visibility="hidden". Test_ODP.odp

from docling.document_converter import DocumentConverter

doc = DocumentConverter().convert("Test_ODP.odp").document
print(doc.export_to_markdown())

Actual:

# Introduction

Overview and Key Objectives

# Key Insights

Main Findings and Takeaways

Expected: the hidden slide 2 ("Key Insights") is not in the default export.

Proposed behavior

Put the content of a hidden slide in ContentLayer.INVISIBLE, the same as hidden ODS sheets and hidden PowerPoint slides. I'd like to send a PR.

Docling version

main @ 21588f5

Python version

3.12.14