Add get_pdf_filename() to API

[jakejackson1]

Description

WIP

Testing instructions

Screenshots

Checklist:

• [ ] I've tested the code.
• [ ] My code is easy to read, follow, and understand
• [ ] My code follows the accessibility standards.
• [ ] My code has proper inline documentation / docblocks.

Additional Comments

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.07%. Comparing base (73750a2) to head (834ef18). Report is 2 commits behind head on development.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1558 +/- ## ============================================ Coverage 76.07% 76.07% ============================================ Files 248 248 Lines 12993 12993 Branches 370 370 ============================================ Hits 9885 9885 Misses 3100 3100 Partials 8 8 ```

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