We could use:
https://github.com/mozilla/pdf.js/blob/c3d08580627471432a6ad0b2fdb948df64126afa/src/display/api.js#L929

and look at bit 4.

The following pdf:
https://orimi.com/pdf-test.pdf
is not editable in neither Acrobat nor Edge nor Foxit and nor Okular.
case 109: 
      case 189: 
        if (!isViewerInPresentationMode) {
          PDFViewerApplication.zoomOut();
        }
        handled = true;
        break;
      case 48: 
      case 96: 
        if (!isViewerInPresentationMode) {
          
          setTimeout(function () {
            
            PDFViewerApplication.zoomReset();
          });
          handled = false;
        }
        break;
      case 38: 
        if (isViewerInPresentationMode || PDFViewerApplication.page > 1) {
          PDFViewerApplication.page = 1;
          handled = true;
          ensureViewerFocused = true;
        }
        break;
      case 40: 
        if (
          isViewerInPresentationMode ||
          PDFViewerApplication.page < PDFViewerApplication.pagesCount
        ) {