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.
if (PDFViewerApplication.secondaryToolbar.isOpen) {
          PDFViewerApplication.secondaryToolbar.close();
          handled = true;
        }
        if (
          !PDFViewerApplication.supportsIntegratedFind &&
          PDFViewerApplication.findBar.opened
        ) {
          PDFViewerApplication.findBar.close();
          handled = true;
        }
        break;
      case 40: 
      case 34: 
        
        if (pdfViewer.isVerticalScrollbarEnabled) {
          turnOnlyIfPageFit = true;
        }
        turnPage = 1;
        break;
      case 13: 
      case 32: 
        if (!isViewerInPresentationMode) {
          turnOnlyIfPageFit = true;
        }
        turnPage = 1;
        break;
      case 39: 
        
        if (pdfViewer.isHorizontalScrollbarEnabled) {