DjVuLibre might be a bit more popular than PDF Reader X. We know about 1 link to it since March 2021 and only 1 link to PDF Reader X. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I suggest that you try with a dedicated PDF viewer, I'm using Adobe Acrobat Reader DC (i.e. The "official" one) but there's a bunch out there, Foxit Reader is another that people sometimes recommend. Source: almost 3 years ago
How likely is it that sioyek can/will be extended to djvu files? It might be a big ask, but I know zathura has an extension that uses djvulibre to make it compatible. As far as I can tell, that's the only thing that I use zathura for that sioyek cannot do (it seems). Source: over 1 year ago
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
WinDjView - WinDjView is a fast, compact and powerful DjVu viewer for Windows with tabbed interface, continuous...
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
RoxyApps eBook Conversion Tool - Convert djvu, epub, fb2, lit, azw, lrf and other eBook files to txt, pdf, pdb, rtf and other formats
Okular - Okular is a universal document viewer based developed by KDE.
Evince - Evince is a document viewer for multiple document formats: PDF, Postscript, djvu, tiff, dvi, XPS...