PDF export fail to export sanskrit characters with serif font-family

Steps to reproduce:

1. Configure the standard wiki with LibreOffice (6.2.4.2 used in this case)
2. Create a new page selecting Type - Page from Office
3. Select the attached document
4. Import with Filter style Deselected
5. Access the page
6. Click on More actions > Export > Export as PDF

Expected results: The PDF is generated properly.

Actual results: Some special characters aren't properly exported eg. "Oḍḍiyāna, Uḍḍiyāna, mukuta" is shown as "O##iy#na, U##iy#na, mukuta", "ālaya" shown as "#laya", "śukla, śveta, haṃsa" shown as "#ukla, #veta, ha#sa"