PdfMerger does not merge outlines of pdf documents with single pages

[fhg-isi]

In the following example, I would expect result.pdf to contain outline items. However, the outline is empty, due to

outline = self._trim_outline(reader, outline, pages)

The individual files first.pdf and second.pdf contain the expected outline entries.

import os

import matplotlib.pyplot as plt
from pypdf import PdfMerger, PdfReader


def main():

    x = [1, 2, 3, 4, 5]
    y = [2, 4, 6, 8, 10]

    fig, ax = plt.subplots()
    ax.plot(x, y)

    save_pdf_with_outline_title(fig, 'first.pdf', 'first_outline_title')

    save_pdf_with_outline_title(fig, 'second.pdf', 'second_outline_title')

    merger = PdfMerger()
    first_pdf = PdfReader('first.pdf')
    merger.append(first_pdf, import_outline=True)

    second_pdf = PdfReader('second.pdf')
    merger.append(second_pdf, import_outline=True)

    merger.write('result.pdf')


def save_pdf_with_outline_title(graph, file_path, outline_title):
    temp_file_path = file_path.replace('.pdf', '_temp.pdf')
    graph.savefig(temp_file_path, bbox_inches='tight')

    merger = PdfMerger()
    temp_pdf = PdfReader(temp_file_path)
    merger.append(temp_pdf, outline_item=outline_title)

    merger.write(file_path)
    os.remove(temp_file_path)


if __name__ == '__main__':
    main()

[stefan6419846]

PyPDF2 and PdfMerger are deprecated, please move to pypdf.PdfWriter. If the issue still persists, please update your code accordingly.

[fhg-isi]

Switching to PdfWriter did the trick. (Switching from pypdf2 to pypdf and updating pypdf from 3.15.2 to 4.2.0 did not help.)

import os

import matplotlib.pyplot as plt
from pypdf import PdfWriter, PdfReader


def main():

    x = [1, 2, 3, 4, 5]
    y = [2, 4, 6, 8, 10]

    fig, ax = plt.subplots()
    ax.plot(x, y)

    save_pdf_with_outline_title(fig, 'first.pdf', 'first_outline_title')

    save_pdf_with_outline_title(fig, 'second.pdf', 'second_outline_title')

    writer = PdfWriter()
    first_pdf = PdfReader('first.pdf')
    writer.append(first_pdf, import_outline=True)

    second_pdf = PdfReader('second.pdf')
    writer.append(second_pdf, import_outline=True)

    writer.write('result.pdf')


def save_pdf_with_outline_title(graph, file_path, outline_title):
    temp_file_path = file_path.replace('.pdf', '_temp.pdf')
    graph.savefig(temp_file_path, bbox_inches='tight')

    writer = PdfWriter()
    temp_pdf = PdfReader(temp_file_path)
    writer.append(temp_pdf, outline_item=outline_title)

    writer.write(file_path)
    os.remove(temp_file_path)


if __name__ == '__main__':
    main()