Remove redundant PDF file opening in loop

[Gustavo R. Ayala (agustavo87)]

Purpose

Remove unnecessary pymupdf.open() call inside the page iteration loop. The PDF was being reopened on every page unnecessarily.

Also adds explicit doc.close() for proper resource cleanup.

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

Remove images converted page_*.png in notebooks and notebooks/Spanish
Run the corresponding sections of chat_pdf_images.ipynb notebooks, until the ## Convert PDFs to images python code block where the pdfs are converted to images (ensure dependencies installed) .

What to Check

Check that the page_*.png files are created correctly (14 pages)

[Gustavo R. Ayala (agustavo87)]

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