The repo appears to contain a copy of Foxit’s/Google’s pdfium along with a UI and lots of abstraction layers/examples for various JavaScript frameworks.
I’m not a JavaScript developer (perhaps there are cultural differences at play?), but in general I think it would be polite to credit the developers of the actual PDF engine.
The repo is marked with the pdfjs and pdfium topics so there is that.
Beyond that, powered by... and similar make sense if the library/engine allows or encourages the behavior.
Absolutely, and I agree, credit is important. I have a whole section in the docs about PDFium and its origins with Foxit/Google: https://www.embedpdf.com/docs/pdfium/introduction.
That’s neat.
I would also mention it in the README.md.