# Description of Changes
Previously, highlight annotations in PDF documents converted to PDF/A
format lost their opacity, resulting in highlights appearing completely
opaque.
This issue stemmed from LibreOffice’s PDF to PDF/A conversion process
and affected both supported PDF/A variants (PDF/A-1B and PDF/A-2B). To
resolve this, a new conversion method was implemented.
Because PDF/A-1B does not support transparency, unlike PDF/A-2B, the
input PDF must be preprocessed to flatten existing transparent objects
when targeting PDF/A-1B.
Changes:
- Preprocess the PDF to handle highlight transparency when converting to
PDF/A-1B;
- LibreOffice's PDF to PDF/A conversion is now only used if fonts are
not embedded or images require flattening;
- If needed, missing fonts and flattened images are imported from the
LibreOffice-converted file;
- The document is traversed to remove elements non-compliant with PDF/A
standards;
- Updated metadata, including all metadata schemes, to ensure full
compliance;
- Added an ICC Profile if one was not already present.
Any challenges encountered:
- Since PDF/A-1B does not support transparency, the best workaround I
found in other conversion tools was to draw close diagonal lines with
the highlight color to simulate transparency, as seem in the example
below.
Closes#3106
Example from the issue:
Original:
PDF/A-1B:
PDF/A-2B:
---
## Checklist
### General
- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings
### Documentation
- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)
### UI Changes (if applicable)
- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)
### Testing (if applicable)
- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.
I tested the changes using a variety of PDF files and verified PDF/A
compliance of the outputs using VeraPDF. While these tests covered
different scenarios and document types, PDF files can vary significantly
in structure and complexity.
As a result, the testing was not exhaustive, and while the results so
far have been compliant, full compliance in all edge cases cannot be
guaranteed.
---------
Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>
