Wrong handling of ligatures

[stefan6419846]

For some PDF files, I am receiving invalid characters as part of the text extraction, especially when ligatures are involved.

Please note that the direct goal of this issue is not to resolve #3376, which could be useful here, but analyze the issue with the font/ligature and possibly fix it.

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
Linux-6.4.0-150600.23.103-default-x86_64-with-glibc2.38

$ python -c "import pypdf;print(pypdf._debug_versions)"
pypdf==6.16.1, crypt_provider=('cryptography', '46.0.5'), PIL=12.1.0

Code + PDF

This is a minimal, complete example that shows the issue:

from pypdf import PdfReader

reader = PdfReader('BSI-TR-03183-1_v1_0_0.pdf')
for index, page in enumerate(reader.pages):
    if index not in {2, 3}:
        continue
    print(page)
    print(page.get_contents().get_data())
    print(page.extract_text().encode())
    print(page.extract_text(extraction_mode="layout"))

The file is available at https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/TechGuidelines/TR03183/BSI-TR-03183-1_v1_0_0.pdf?__blob=publicationFile&v=3

Traceback

There is no traceback, but the first extracted text is:

Technical Guideline TR-03183-1\nFederal Of\xee\x80\x80ce for Information Security 3

The wrongly interpreted text looks like this if printed as string instead of bytes:

Federal Ofce for Information Security

[stefan6419846]

As an additional note: pdftotext handles it correctly, copying from Evince works as well, the display in Evince when selecting the characters is wrong.