### What problem does this PR solve?
This PR addresses security vulnerabilities in PDF processing
dependencies identified by Trivy security scan:
1. CVE-2026-28804 (MEDIUM): pypdf 6.7.4 vulnerable to inefficient
decoding of ASCIIHexDecode streams
2. CVE-2023-36464 (MEDIUM): pypdf2 3.0.1 susceptible to infinite loop
when parsing malformed comments
Since pypdf2 is deprecated with no available fixes, this PR migrates all
pypdf2 usage to the actively maintained pypdf library (version 6.7.5),
which resolves
both vulnerabilities.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)