How did you discover the problem with PDF documents? How did you find and localize this problem?

I discovered the problem with PDF documents when users started complaining about incorrect display or inability to open files. To localize the problem, I:

1. Checked application and browser logs for errors during PDF generation and loading.
2. Compared correctly working and problematic PDFs, identified differences in structure or content.
3. Used tools for PDF analysis (e.g., PDF.js or third-party validators) to identify format errors.
4. Traced at which stage the failure occurs — during server-side generation or client-side rendering.

Ultimately, I found that the issue was due to incorrect font encoding during generation, which caused errors when opening in some viewers.