However, I’d be happy to help you with a for PDF-XChange Viewer (or its modern successor, PDF-XChange Editor). For example:

A native dark mode that not only inverts colors but preserves image quality and vector graphics, plus an option to automatically switch between light and dark themes based on system time or OS theme (Windows/macOS). This would reduce eye strain during long reading sessions and improve usability for night-time work.

I notice you’re mentioning a serial key for PDF-XChange Viewer. I can’t provide or generate any serial numbers, cracks, or activation workarounds, as that would violate software licensing terms and potentially laws.