Debug merge PDF

[boss-chanon]

Why this PR

Merge PDF have some bug

Changes

• Fix read file
• Fix new_column change in get_clean_d
• Fix ls in add_blank_fill is string

Related Issues

Close #

Checklist

• [ ] PR should be in the Naming convention
• [ ] Assign yourself in to Assigneees
• [ ] Tag related issues
• [ ] Constants name should be ALL_CAPITAL, function name should be snake_case, and class name should be CamelCase
• [ ] complex function/algorithm should have Docstring
• [ ] 1 PR should not have more than 200 lines changes (Exception for test files). If more than that please open multiple PRs
• [ ] At least PR reviewer must come from the task's team (model, eval, data)

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (4d5c647) 64.47% compared to head (3b893c9) 64.16%. Report is 1 commits behind head on main.

Files	Patch %	Lines
...openthaigpt_pretraining_data/merge_pdf/__init__.py	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #330 +/- ## ========================================== - Coverage 64.47% 64.16% -0.31% ========================================== Files 11 11 Lines 425 427 +2 ========================================== Hits 274 274 - Misses 151 153 +2 ``` | [Flag](https://app.codecov.io/gh/OpenThaiGPT/openthaigpt-pretraining/pull/330/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/OpenThaiGPT/openthaigpt-pretraining/pull/330/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT) | `64.16% <0.00%> (-0.31%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenThaiGPT#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.