The catalog.json profile
File: media/plg_system_wtpdfjs-config/catalog.json. Light theme and paired pages. For a separate cover, try spreadModeOnLoad=2; check the page order in your PDF.
JSON example
{
"defaultZoomValue": "page-fit",
"viewerCssTheme": 1,
"sidebarViewOnLoad": 1,
"scrollModeOnLoad": 0,
"spreadModeOnLoad": 1,
"viewOnLoad": 1
}