Bug when exporting page with Polish characters to PDF

[fmakowski]

• BookStack Version: v0.18.5
• PHP Version: php:7.1.10-apache (I guess? I am using solidnerd/docker-bookstack)
• MySQL Version: 5.7.20

Expected Behavior

When I export a file to PDF, the UTF-8 coding is preserved and I can see Polish chatacters.

Just like on the site:

Current Behavior

When I export a file to PDF, and it consists of language-specific characters (śćńąę etc.), there will be ? instead:

The issue is not present when exporting to HTML or to text file:

Steps to Reproduce

1. Create a page with the following title and contents:

   Just tęśtińg Półish chąraćters
   Iń thę ćóntęnt ąś węłł.

2. Export to PDF.

Additional comments

I have checked other PDF viewers - they are not the reason it looks that way.

Also, interestingly, "ó" is parsed properly (but maybe it's included in a character set that is somehow more compatible with the standard one).

I would also rule out the font, as each document is using the same one.

[fmakowski]

I see that this is a similar bug to the one in #148. For that reason, I am closing the issue, but referecing it in the other one.

[alexwoo-awso]

PDF export title glyphs break because headings use the heading font var and DOMPDF falls back to base fonts without Polish glyphs. I added a PDF-only heading font override to DejaVu Sans in export-styles.scss; verified Polish title characters render correctly. I have opened a PR with the fix -> #6069