[Bug]: Existing text is completely replaced with other characters

[david-sledge]

Describe the bug

Found an issue with certain PDFs that already have text where the text is replaced with other characters and renders the PDFs unreadable. This happens with the --redo-ocr and --skip-text flags. Attached are (a) a sample PDF (b) the results of it being OCRed, and (c) a zip file containing everything needed to reproduce the issue.

Steps to reproduce

1. Download the tarball to a linux machine with Docker installed.
2. Run the following command chain: tar -xzf bad-pdf-example.tar.gz && cd bad-pdf-example && docker run --rm -v .:/root/test-files -it $(docker build -q -t ocrmypdf-test .) && docker rmi ocrmypdf-test:latest
3. Open test-redo-ocr-result.pdf and test-skip-text-result.pdf

Files

test.pdf test-redo-ocr-result.pdf test-skip-text-result.pdf bad-pdf-example.tar.gz

How did you download and install the software?

Linux package manager (apt, dnf, etc.), Docker container

OCRmyPDF version

16.3.1

Relevant log output

tesseract 5.4.1
 leptonica-1.82.0
  libgif 5.1.9 : libjpeg 8d (libjpeg-turbo 2.1.1) : libpng 1.6.37 : libtiff 4.3.0 : zlib 1.2.11 : libwebp 1.2.2 : libopenjp2 2.4.0
 Found AVX512BW
 Found AVX512F
 Found AVX2
 Found AVX
 Found FMA
 Found SSE4.1
 Found OpenMP 201511
 Found libarchive 3.6.0 zlib/1.2.11 liblzma/5.2.5 bz2lib/1.0.8 liblz4/1.9.3 libzstd/1.4.8
 Found libcurl/7.81.0 OpenSSL/3.0.2 zlib/1.2.11 brotli/1.0.9 zstd/1.4.8 libidn2/2.3.2 libpsl/0.21.0 (+libidn2/2.3.2) libssh/0.9.6/openssl/zlib nghttp2/1.43.0 librtmp/2.3 OpenLDAP/2.5.17
OCRmyPDF version:
16.3.1
Scanning contents     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
    1 skipping all processing on this page                                                                                                                                                                                      _pipeline.py:330
OCR                   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
Postprocessing...                                                                                                                                                                                                                     ocr.py:144
PDF/A conversion      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
Some input metadata could not be copied because it is not permitted in PDF/A. You may wish to examine the output PDF's XMP metadata.                                                                                             _metadata.py:62
Linearizing           ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 100/100 0:00:00
Recompressing JPEGs   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
Deflating JPEGs       ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
JBIG2                 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
Image optimization ratio: 1.00 savings: 0.0%                                                                                                                                                                                    _pipeline.py:989
Total file size ratio: 0.06 savings: -1515.7%                                                                                                                                                                                   _pipeline.py:992
Output file is a PDF/A-2B (as expected)                                                                                                                                                                                           _common.py:441
Scanning contents     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
    1 redoing OCR                                                                                                                                                                                                               _pipeline.py:327
OCR                   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
Postprocessing...                                                                                                                                                                                                                     ocr.py:144
PDF/A conversion      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 1/1 0:00:00
Some input metadata could not be copied because it is not permitted in PDF/A. You may wish to examine the output PDF's XMP metadata.                                                                                             _metadata.py:62
Linearizing           ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 100/100 0:00:00
Recompressing JPEGs   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
Deflating JPEGs       ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
JBIG2                 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━   0% 0/0 -:--:--
Image optimization ratio: 1.00 savings: 0.0%                                                                                                                                                                                    _pipeline.py:989
Total file size ratio: 0.06 savings: -1554.7%                                                                                                                                                                                   _pipeline.py:992
Output file is a PDF/A-2B (as expected)