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 (cmd === 0) {
    let turnPage = 0,
      turnOnlyIfPageFit = false;
    switch (evt.keyCode) {
      case 38: 
      case 33: 
        
        if (pdfViewer.isVerticalScrollbarEnabled) {
          turnOnlyIfPageFit = true;
        }
        turnPage = -1;
        break;
      case 8: 
        if (!isViewerInPresentationMode) {
          turnOnlyIfPageFit = true;
        }
        turnPage = -1;
        break;
      case 37: 
        
        if (pdfViewer.isHorizontalScrollbarEnabled) {
          turnOnlyIfPageFit = true;
        }
      
      case 75: 
      case 80: 
        turnPage = -1;
        break;
      case 27: