Incorrect text when copying from pdf and pasting into a text editor

[EvgeniyBudaev]

Describe the bug
We connect the font via Font.register. Text 123ff456fi987. Copy in the downloaded pdf file 123ff456fi987. Paste it into a text editor. We get 123f456f987 instead of 123ff456fi987. Bottom line: there is a bug with the symbols ff, fi with plug-in fonts.

To Reproduce
Steps to reproduce the behavior including code snippet (if applies):

1. https://github.com/EvgeniyBudaev/react-pdf-renderer
2. Dowload pdf file with text: 123ff456fi987
3. Copy in the downloaded pdf file 123ff456fi987
4. Paste it into a text editor.
5. 5. We get 123f456f987 instead of 123ff456fi987

You can make use of react-pdf REPL to share the snippet

Expected behavior
123ff456fi987

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [Windows, Ubuntu]
• Browser [chrome]
• React-pdf version [e.g. v4.1.6]