Hi Alexandr Mykhailov,
Thank you for your patience. The reported behavior occurs because the tested PDF documents use custom fonts to render the text. To resolve this, we request that you add the respective custom fonts as TTF files using the customFonts API in the PDF Viewer.
We have attached a working sample project along with the user guide (UG) for your reference. Please review these and let us know whether the issue is resolved from your end after applying the suggested changes.
UG for add custom fonts in PDF Viewer
Snapshots:

Regards,
Venkada Subramanian D
Attachment:
Custom_Fonts_9fd607b0.zip