If you downloaded GSview 5.0 some time ago (specifically versions prior to the February 2024 update), you might still be seeing the registration prompt. You have two options:
The engine behind Gsview is Ghostscript. You can use it directly: Gsview 5.0 Registration Key
For a GUI, combine with SumatraPDF or Evince. If you downloaded GSview 5
Best lightweight alternative. Supports PDF, PS, DjVu, XPS, CBZ, CBR. Portable, fast, and respects privacy. For a GUI, combine with SumatraPDF or Evince
This is the best solution. Download the latest version of GSview 5.0 from the official Ghostgum Software website. By installing the newest release, the registration prompts will disappear entirely, and you will have the most secure and stable version of the software.