The mobile.json profile
File: media/plg_system_wtpdfjs-config/mobile.json. Suitable for a narrow iframe. Your code selects this profile; it is not automatic screen detection and does not resize the container.
JSON example
{
"defaultZoomValue": "page-width",
"sidebarViewOnLoad": 0,
"scrollModeOnLoad": 3,
"spreadModeOnLoad": 0,
"viewOnLoad": 1
}